Thucydiaceae Fam. Nov., with a Review and Reevaluation of Paleozoic Walchian Conifers

Thucydiaceae Fam. Nov., with a Review and Reevaluation of Paleozoic Walchian ConifersAuthor(s): Genaro R. Hernandez‐Castillo, Gar W. Rothwell, and Gene MapesSource: International Journal of Plant Sciences, Vol. 162, No. 5 (September 2001), pp. 1155-1185Published by: The University of Chicago PressStable URL: http://www.jstor.org/stable/10.1086/321920 .

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1155

Int. J. Plant Sci. 162(5):1155–1185. 2001.� 2001 by The University of Chicago. All rights reserved.1058-5893/2001/16205-0014$03.00

THUCYDIACEAE FAM. NOV., WITH A REVIEW AND REEVALUATIONOF PALEOZOIC WALCHIAN CONIFERS

Genaro R. Hernandez-Castillo,1,* Gar W. Rothwell,† and Gene Mapes†

*Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada; and †Departmentof Environmental and Plant Biology, Ohio University, Athens, Ohio 45701, U.S.A.

Abundant fossils of a single conifer species occur in a Pennsylvanian-age deposit of eastern North America,providing the opportunity to describe a biological taxon of primitive conifers as well as to clarify the uncertaintaxonomy and systematics of walchian conifers. Thucydia mahoningensis gen. et sp. nov. is represented byup to three orders of interconnected vegetative and fertile shoots that are preserved as coalified compressionswith cuticles; some also display internal anatomy. The plant has an orthotropic stem, with two orders ofplagiotropic lateral branches that all bear helically arranged simple leaves. Ovulate fructifications consist ofcompact zones of bracts with axillary ovuliferous dwarf shoots on otherwise vegetative branches. Pollen conesare compound shoots comprising helically arranged dwarf shoots in the axils of bracts on a main axis.Polliniferous dwarf shoots produce sterile scales, sporophylls with a terminal pollen sac, and in situ Poton-ieisporites grains. Stems have an endarch eustele with dense wood, periderm, and resin canals in the pith.There are two adaxial stomatal zones on vegetative leaves, but stomata are distributed over the entire adaxialsurface of bracts and sterile scales. Thucydia is the only conifer with ovuliferous fertile zones, compoundpollen cones, and dissimilar stomatal distributions on vegetative and fertile leaves. This novel combination offeatures characterizes the Thucydiaceae fam. nov. The currently confused state of primitive conifer taxonomyis reviewed, nomenclature is clarified, and revised approaches for inferring relationships are proposed. Thucydiaprovides a benchmark for developing sound taxonomic concepts and useful criteria for identifying specimensof walchian species and for resolving phylogenetic relationships among fossil and living conifers.

Keywords: conifer systematics, compound pollen cone, fossil, Paleozoic, walchian conifer.

Introduction

Conifers have played a major role in terrestrial ecosystemssince the end of the Carboniferous. They form the dominantcanopy vegetation from the Permian to the Cretaceous andcomprise a major component of modern mountain and borealforests (Florin 1963). The most ancient Permo/Carboniferousspecies grew on apparently well drained basinal slopes of theEuramerican equatorial Tropics (Florin 1938–1945, 1963;Rothwell et al. 1997) and are often referred to as walchianconifers (Mapes 1987). Numerous species have been describedfrom Europe, North America, and North Africa (Florin1938–1945). Smaller numbers of questionably walchian spec-imens also occur in Angara, Cathaysia, and Gondwana (Florin1938–1945, 1950, 1964), but most identifications from theserealms are tentative and require confirmation (e.g., Geng andHilton 1999).

Walchian cones have leafy ovuliferous dwarf shoots (Florin1951). Most show obvious sporophylls (Mapes and Rothwell1991), and individual species display wide ranges of variationin vegetative leaf morphology and leaf size from branch tobranch. Pollen cones are thought to be similar to those of themodern Pinaceae (Florin 1950), but this may be incorrect(Mapes and Rothwell 1998; Rothwell and Mapes 2001). Some

1 Author for correspondence; e-mail [email protected].

Manuscript received December 2000; revised manuscript received April 2001.

walchian species have forked leaves on the stem and penul-timate branches and simple leaves on ultimate shoots (Florin1950), but others have simple leaves throughout. All of themost completely known species have progressively smallerleaves on successively more distal branches (e.g., Florin 1950;Clement-Westerhof 1984), and there are age-related variationsin the angles of branching and leaf insertion for at least somespecies (Hernandez-Castillo 2000).

Numerous walchian species have been described from Penn-sylvanian/Upper Carboniferous and Permian deposits of Eur-america (Clement-Westerhof 1984) and are assigned to severalgenera and families (Mapes and Rothwell 1991). The earliestand most numerous descriptions are of European specimens(Dijkstra 1975), in which species are based primarily onmorphological characters of vegetative branches (Florin1938–1945; Visscher et al. 1986). Unfortunately, these de-scriptions overlap with each other to such a great extent thatmany species are of questionable validity (Clement-Westerhof1984; Visscher et al. 1986). Ovulate cones and pollen coneshave been assigned to some species (Renault 1885; Florin1938–1945; Clement-Westerhof 1984; Mapes and Rothwell1984; Kerp et al. 1990). However, pollen cones are popularlyregarded as having a uniform structure (Florin 1950, 1951;Clement-Westerhof 1984), and ovulate cones with specificallydiagnostic characters have thus far been described for only asmall number of species (Renault 1885; Florin 1938–1945;Clement-Westerhof 1984; Kerp et al. 1990).



1156 INTERNATIONAL JOURNAL OF PLANT SCIENCES

Fig. 1 Map of collecting locality; location of the abandoned 7-11 mine on eastern margin of Ohio indicated by an asterisk

Florin (1951) has developed taxonomically informativecuticular characters that are widely regarded as being specif-ically diagnostic for walchian conifer species (Florin 1927,1938–1945, 1950; Clement-Westerhof 1984). Cuticles haveallowed for the confident separation of Ernestiodendron fili-ciforme (Schlotheim) Florin from species of Lebachia Florin(Florin 1938–1945). However, in practice, these data have notbeen useful for separating the most closely related species, inwhich cuticular characters overlap at least as completely as domorphological characters (e.g., table 3). With the exception ofthe genus Ortiseia Florin (Clement-Westerhof 1984), contrast-ing combinations of specific characters have not been devel-oped to help identify specimens of the most similar walchianconifers, and diagnostic ranges of variation in morphologicaland cuticular characters have not been tabulated for a singlewalchian species.

This situation is further complicated by nomenclatural ir-regularities that have led to a great deal of confusion anddisagreement regarding the legitimate names for some of themost well known genera and species (Clement-Westerhof1984; Kerp et al. 1990; Mapes and Rothwell 1991). At present,many specific identifications rely more heavily on the opinionof the researcher than on diagnostic characters. Therefore,most newly discovered specimens of walchian conifers cannotbe assigned to a species with confidence. As a result, the sys-tematic framework within which walchian conifers are un-derstood remains weakly developed, the concepts of generaand families are confused and overlapping, legitimate namesfor genera and species are in dispute, and species concepts areoften only minimally useful for the identification of specimens.

This situation is particularly frustrating when it comes toattempts to identify and assign appropriate names to the ex-cellently preserved North American walchian conifer materialthat has been under investigation for the past 20 yr (Rothwell1982; Mapes and Rothwell 1984, 1988, 1991, 1998; Mc-Comas 1988; Mapes et al. 1989; Rothwell et al. 1997; Her-nandez-Castillo 2000; Liu et al. 2000). These studies focus on

large numbers of specimens to delimit individual species ofplants from interconnected organs and common suites of veg-etative and reproductive characters (Rothwell et al. 1997). De-scriptions are based on pollen cones, ovulate fructifications,and vegetative remains, and some include characters from in-ternal anatomy as well as morphology and cuticles. Never-theless, in the absence of well-established criteria for identi-fying specimens and assigning them to recognized species orfor determining how many species occur in mixed walchianconifer assemblages, it usually has been impossible to deter-mine whether such material represents one or more new speciesor additional specimens of previously established species.

This study is part of an ongoing program to develop work-able taxonomic concepts for Paleozoic fossil conifers, to pre-sent these concepts in the form of testable hypotheses, and toestablish a solid database for characterizing species and infer-ring systematic relationships by cladistic methodology.To achieve these goals, we are conducting detailedspecies-by-species studies of Paleozoic conifers and other con-iferophytes. In this article, we characterize the morphology,cuticular features, and internal anatomical characters of morethan 250 vegetative and fertile conifer specimens from a singlebiotic assemblage (McComas 1988, 1989). Many of the organsare interconnected, and all of the specimens of each organconform to a continuous range of variation for all characters.These demonstrate that only one species of conifers is presentin the assemblage. This monotypic conifer assemblage allowsus to determine with confidence that the material represents anew walchian, Thucydia mahoningensis gen. et sp. nov., andto document several characters that previously have been un-known for conifers. Diagnostic characters of Thucydia includeovulate fructifications that consist of compound fertile zonesin the midregion of ultimate branches, compound pollen cones,resin canals with an epithelial lining, and distinctive stomataldistributions.

Because this combination of characters is novel and fallsoutside the circumscription of currently recognized families of



HERNANDEZ-CASTILLO ET AL.—PALEOZOIC WALCHIAN CONIFERS 1157

Table 1

Comparative Morphological and Cuticular Characters of Thucydia mahoningensis Leaves

Organ/charactersShape

(side view)Shape

(face view)Length(mm)

Width(mm)

Stomataldistribution(all adaxial)

Stomatalcomplex

size

Papillae onsubsidiary

cells

Papillateepidermal

cells

Number ofsubsidiary

cells

Antepenultimateleavesa Linear or

S shapedNarrow

triangular tolinear

14.0–17.0 2.8–3.0 ? ? ? ? ?

Penultimateleaves Linear or

S shapedNarrow

triangular tolinear

5.0–12.5 1.0–1.5 Two bands 41 # 40 Predominantlyoverarching

Yes 6–8

Ultimate leaves(proximalregion) Linear or

S shapedNarrow

triangular tolinear


Yes 6–8

Ultimate leaves(distal region) Linear or

S shapedNarrow

triangular tolinear


Yes 6–8

Bracts of pollencone Linear or

S shapedNarrow

triangular tolinear

3.0–5.0 0.8–2.0 On the wholesurface

30 # 26 Predominantlyerect

Yes 4–8

Sterile scales ofpollen cone Linear or

S shapedNarrow

triangular tolinear



Yes 4–8

Bracts of ovulatezones Linear or

S shapedNarrow

triangular tolinear



Yes 4–6

Sterile scales ofovulate zones Linear or

S shapedNarrow

triangular tolinear



Yes 4–6

a Measurements from antepenultimate leaves on holotype.

conifer plants, we also propose the new family Thucydiaceae.Using T. mahoningensis as a benchmark for developing specificconcepts for the most ancient conifer plants, we review thecurrent state of walchian conifer taxonomy and nomenclature,assess the usefulness of different taxonomic characters, andpropose an agenda for improving primitive conifer taxonomyand systematics. This material also provides the first oppor-tunity to quantify the ranges of variation that occur in nu-merous characters for a single species of walchian conifers, tointerpret growth architecture for the many ancient conifers, tocharacterize cuticular fine structure from different organs ofthe same fossil conifer, and to infer systematic relationshipsamong walchian species (Hernandez-Castillo 2000). These lat-ter studies are in preparation for presentation separately.

Material and Methods

Specimens were recovered from an abandoned strip mineformerly operated by the 7-11 Coal Company near East Liv-

erpool in Columbiana County, Ohio (fig. 1; McComas 1988).Conifer remains occur in 1.5 M of finely laminated, argilla-ceous, organic, black, silty shale (McComas 1989). These sed-iments are interpreted as freshwater units that are boundedlaterally by cross-bedded sandstones and that occupy a paleo-topographic low suggestive of an abandoned river channel(McComas 1988). Stratigraphically, the deposit is located be-tween two recognized markers, the Mahoning coal and theBrush Creek marine unit (McComas 1988, 1989). Identifica-tion of the coal as the Mahoning by R. M. Kosanke (U.S.Geological Survey report file 0-86-23D) is based upon paly-nological assessment (McComas 1988, 1989). The Mahoningcoal is the lowest coal seam of the Conemaugh Group in theAppalachian Basin (Phillips et al. 1985). The Brush Creek isrecognized as the earliest marine unit of the Conemaugh Group(Phillips et al. 1985; McComas 1989), but the age of the fossilmaterial is in dispute. These units traditionally have been in-terpreted as either Desmoinesian (Westphalian D) or Mis-sourian (Stephanian A; McComas 1989), but an alternative






Fig. 2 Morphology of orthotropic and plagiotropic branching systems of Thucydia mahoningensis. A, Specimen showing three orders ofbranching. The largest branch (antepenultimate) shows penultimate branches attached on several radii (small arrows) and is therefore orthotropic.Ultimate branches are attached to the plagiotropic penultimate branches in two rows (between large arrows). Note that helically arranged simpleleaves on the penultimate branches (upper left) are distinctly larger than those of the ultimate branches (center right). The number of ultimateshoots per penultimate branch is variable because of incomplete preservation. OUPH 13411 (G200) #2; cm. B, Large plagiotropicscale p 1branching system composed of a penultimate shoot and 92 ultimate branches. Both shoots are covered by helically arranged simple leaves. Thebranching system is preserved by coalified compression and impression, with partial permineralization of some ultimate shoots (pp). Note theovate shape of the branching system. OUPH 13412 (GC-1) #0.3; cm.scale p 5

interpretation has been proposed by Wagner and Lyons (1997).According to those authors, the lower Conemaugh flora ofColumbiana County of Ohio is strongly reminiscent ofthe European Upper Carboniferous/Permian transition (i.e.,Autunian).

The material consists of 365 specimens including 342 veg-etative shoots, 22 compound ovulate zones, and one com-pound pollen cone, all of which are preserved as coalified com-pressions with cuticular remains. Segments of some specimensare permineralized with pyrite, preserving internal cellularanatomy. Morphological characters were observed with a dis-secting microscope. Dissecting needles were used to removerock matrix covering the fossils. Some specimens were mac-erated in hydrofluoric acid to reveal characters not preservedon rock surfaces and to facilitate cuticular preparations. Mac-erations were stopped periodically to record structural featuresat successive levels. Specimens were neutralized by rinsing andwere immersed in alcohol and/or water for observation andimage capture. Some images were digitized and used as tem-plates for line drawings to aid in the interpretation of mor-phological characters. Anatomical features of permineralizedshoots were prepared using conventional wafering techniquesfor pyrite (Stein et al. 1982) and were then mounted on mi-croscope slides and observed with reflected light.

Cuticular preparations were made by modifications of tech-niques for very dark colored Paleozoic cuticles (Kerp 1990).Cuticles were separated from the rock by chemical macerationwith hydrofluoric acid at different concentrations (50%, 25%,and 10%). After liberation from the rock matrix, the fossilmaterial was bleached with wet and dry Schulze’s reagents(Kerp 1990), dehydrated in an alcohol series, and eithermounted on microscope slides in Eukitt mounting medium (O.Kinder GMBH and Co., Freiburg) or placed on specimen stubsand coated with gold for examination with the scanning elec-tron microscope (SEM).

Multiple measurements of several structures were recordedto assess the ranges of variation among the different vegetativeshoots of the plant. Morphological characters include lengthand width of penultimate and ultimate branches; number ofultimate shoots per penultimate shoot; branching angle; length,width, and thickness of leaves at the proximal and distalregions of ultimate shoots; and angles of separation of leavesat the proximal and distal regions of ultimate shoots (Her-nandez-Castillo 2000; table 2). Cuticular characters measuredinclude stomatal distribution patterns, stomatal complex struc-ture and size, subsidiary cell number, and the nature and dis-tribution of epidermal trichomes and papillae (tables 1, 3).Images were captured digitally and were processed with AdobePhotoshop. Low-magnification images were captured to create

a digital database of vegetative and reproductive shoots. Im-ages were also used to measure penultimate and ultimateshoots and individual leaves.

Because of disagreements regarding the taxonomic assign-ments of specimens and regarding the legitimacy of somenames of walchian conifers, the nomenclature employed in thisstudy differs from that of some of the latest studies by otherresearchers (Clement-Westerhof 1984, 1987, 1988; Visscher etal. 1986; Kerp et al. 1990; Kerp and Clement-Westerhof 1991).The names we adopt reflect the most rigorous concepts ofwalchian conifer taxa at all ranks and are the valid names foreach taxon, as stipulated by the International Code of Botan-ical Nomenclature (St. Louis Code) 2000 (Greuter et al. 2000).Two exceptions are explained in the “Discussion.” In general,these names follow Florin (1927, 1938–1945), with some sub-sequent changes by more recent authors. A summary of bothvalid taxonomic and nomenclatural usage and names that havebeen proposed in error are presented by Mapes and Rothwell(1991) and are elaborated further in the “Discussion.”

Systematic Descriptions

Class—Spermatopsida

Order—Voltziales

Family—Thucydiaceae fam. nov.

Familial diagnosis. Small, eustelic coniferous trees withdense wood and resin canals in pith. Helically arranged simpleleaves on all orders of branching. Fertile organs consisting ofcompound pollen cones and compound ovulate fertile zonesoccurring between vegetative zones on branch. Pollen coneswith helically arranged bracts and axillary dwarf shoots; sterilescales borne toward bract and laterally; sporophylls with oneterminal erect pollen sac borne toward cone axis. Prepollengrains monosaccate, eusaccate. Ovulate dwarf shoots bilateral,with sterile scales all around base of dwarf shoot; sporophyllsterminal with recurved apex, each with apical inverted ovule.Ovules flattened, with peripheral wing.

Type Genus—Thucydia gen. nov.

Generic diagnosis. Characters of genus those of family.Plants with orthotropic stems and plagiotropic lateralbranches. Stomata in two adaxial bands on foliar leaves, dis-tributed all across adaxial surface of bracts and sterile scales.Pollen cone with simple bracts with dentate margins; sterilescales linear, decurrent with dentate margins; sporophylls po-sitioned adjacent to cone axis; prepollen elliptical-circular with




bent monolete suture. Ovuliferous dwarf shoots free from sim-ple bract; sterile scales simple, decurrent, linear, with dentatemargins; sporophylls linear, fanning outward distally.

Type Species—Thucydia mahoningensis sp. nov.

Specific diagnosis. Characters of species those of genus.Simple leaves 14.0–17.0 mm long, 2.8–3.0 mm wide, on an-tepenultimate branches 5.0–12.5 mm long, 1.0–1.5 mm wide,on penultimate branches 3.0–6.0 mm long, 0.4–0.5 mm wide,on ultimate branches; adaxial stomata, six to eight subsidiarycells with overarching and erect papillae; abaxial trichome ba-ses present. Pollen cone ca. 16.0 cm long, 6.0 mm wide; bracts3–5 mm long, 0.8–2.0 mm wide; stomata with four to eightsubsidiary cells; papillae numerous and erect. Polliniferousdwarf shoots with five to eight sterile scales 0.6–1.1 mm long,0.2–0.4 mm wide, mucronate; stomata with four to eight sub-sidiary cells and erect papillae. Pollen sacs ellipsoidal, atten-uate, rounded, 0.8–1.2 mm long, 0.3–0.6 mm wide. Grains60–130 mm, with two parallel crescent-shaped folds at sidesof the central body. Ovulate fertile zones 3.0–4.5 cm long,0.9–1.5 cm wide; bracts 8.0–11.0 mm long, 1.0–1.5 mm wide,linear and S shaped, decurrent, mucronate; trichome basesregularly spaced; stomata evenly distributed, with four to sixsubsidiary cells and erect papillae. Axillary ovulate shoots8.0–9.0 mm long, 6.0–7.5 mm wide, with 10–15 sterile scalesand three to four sporophylls. Sterile scales 2.0–5.0 mm long,0.3–0.6 mm wide, helically arranged around shoot, attachednear base; stomata with four to six subsidiary cells and erectpapillae. Sporophylls 3.0–4.0 mm long, 1.0–1.5 mm wide,with numerous papillae. Seeds oval to elliptical, 2.0 mm long,1.0 mm wide.

Holotype. Specimen OUPH-13450 (GR-1), figures 10Dand 11E, here designated the holotype; reposited in the OhioUniversity Paleobotanical Herbarium.

Paratypes. External morphology of vegetative shoots(G200) OUPH-13411 (fig. 2A); cuticles OUPH-13426 (M2019u1) (fig. 6A, 6L); OUPH-13427 (M2006) (fig. 6B, 6C, 6K,6M); OUPH-13429 (G1A3) (fig. 6E, 6F, 6H, 6N). AnatomyOUPH-13424 (M1451 a8) (fig. 5D); OUPH 13425 (M1454f3) (fig. 5E); OUPH-13437 (M-1454 f17) (fig. 7A); OUPH-13438 (M2019 b10) (fig. 7B); (M2019 c1) OUPH-13439 (fig.7C); (M2019 c2) OUPH-13440 (fig. 7D); OUPH-13444(M2019 b4) (fig. 7I, 7N, 7O); OUPH-13446 (M2019 c3) (fig.7L, 7M). Compound pollen cone OUPH-13457 (G82) (fig. 8A,8B); OUPH-13458 (G82) (fig. 8C); OUPH-13457 (G82) (fig.8D); OUPH-13460 (G82) (fig. 8E, 8G; fig. 9A, 9B); G82(OUPH-13461) (fig. 8F; fig. 9C, 9E); OUPH-13462 (G82-pcp6) (fig. 9D); OUPH-13463 (G82-pcp5) (fig. 9F); OUPH-13465 (G82-pcp4) (fig. 9H). Fertile zones OUPH-13447 (GR-11) (fig. 10A); OUPH-13451 (GR-17) (figs. 10E, 11C);OUPH-13455 (GR-16) (fig. 13A, 13B, 13G). The specimensare reposited in the Ohio University PaleobotanicalHerbarium.

Locality. Abandoned strip mine of the 7-11 Coal Com-pany, located north of East Liverpool on Ohio Route 7, 1.1km north of the junction with Ohio Route 11 in the S 1/2,NW 1/4, Sec. 13, T.10, R.2 W, West Point Quadrangle, Mad-ison Township, Columbiana County, Ohio (fig. 1 of McComas1988).

Lithology and stratigraphy. Terrestrial black shale be-tween the Mahoning coal and the Brush Creek marine siltyunit, Conemaugh Group, Ohio.

Probable age. Late Pennsylvanian (Stephanian A).Etymology. The generic name honors Thucydides (vou-

kudidh�), one of the most important historians in ancientGreece, who was born in Athens and was the first to write atext to be read, not recited. The specific epithet refers to theMahoning coal.

Description

Thucydia mahoningensis is represented by several orders ofvegetative and fertile branches, including several ovulate fertilezones and one pollen cone. Most specimens are preserved asisolated ultimate or penultimate shoots, but 63 specimens dis-play organic connection between at least two orders of branch-ing (figs. 2–4). One specimen has three orders of attachedvegetative branches (figs. 2A, 3). Several specimens consist ofovulate branches with vegetative basal and apical regions (fig.10), and two specimens show ovulate branches attached to alarger axis (fig. 10B, 10D). Because some parts of several pen-ultimate and ultimate shoots are preserved as pyrite permin-eralizations (figs. 2B, 4B), morphological, cuticular, and an-atomical characters are all known from the same specimensof both branching orders. Leaves on all orders of branchingare simple and are helically arranged (figs. 2A, 3).

Vegetative Branches

The specimen with three attached orders of vegetativebranches (fig. 2A) shows five penultimate branches that are8.0–11.0 cm long and 1 mm wide, four of which are in organicconnection to the antepenultimate stem (figs. 2A, 3). The fifthpenultimate shoot extends away from the antepenultimatebranch at an angle that indicates that it was attached just belowthe base of the preserved segment (figs. 2A, 3). Penultimatebranches are all attached to the antepenultimate stem on dif-ferent radii and are inserted at distances of 4.0–7.0 mm (fig.2A). This demonstrates the occurrence in Thucydia of an or-thotropic branching system that is comparable to the stems ofliving Araucaria species (Halle et al. 1978). The antepenulti-mate shoot is wider than the rest of the branches (7 mm).Penultimate shoots are 1.0–1.6 mm wide, whereas ultimateshoots are 0.5–1.6 mm wide.

Penultimate stems range in diameter from 3.0 to 9.0 mm atthe base and from 1 to 3 mm near the apex, and numerousspecimens show ultimate shoots attached in a regular two-ranked arrangement (figs. 2–4) forming pinnate plagiotropicunits. These units display wide ranges of variation in overallsize, shape, angles of branching, leaf size, and leaf shape (figs.2, 4). They are widest near the base and typically taper to apoint (figs. 2B, 4A). Plagiotropic shoots range from 2.5 to38.0 cm in length and from 6.0 to 21.0 cm in width, includingboth rows of ultimate shoots and the penultimate stem. Thesize of the branching systems is positively correlated with thenumber of ultimate branches borne on the penultimate stem(fig. 2B; fig. 4A, 4C). A large plagiotropic branch may bearup to 92 ultimate shoots (fig. 2B). In contrast, one of thesmallest branching systems bears fewer than 20 ultimate shoots




Fig. 3 Thucydia gen. et sp. nov. Digitized tracing of specimen in fig. 2A showing three orders of branching. Orthotropic antepenultimatestem (large arrow) bears plagiotropic branching systems with two rows of ultimate shoots attached (small arrows). Note that leaves on allbranches are simple and that leaves on ultimate shoots are smaller than those on penultimate and antepenultimate branches.

(fig. 4F). Interbranch distance is very similar among the dif-ferent branching systems, characteristically ranging from 1.0to 1.5 cm. Ultimate branches are typically equidistant alongthe stem (fig. 4C–4E), but there is some variation (figs. 2B,4A).

The overall shape of plagiotropic branching systems is cor-related with both the angles of insertion of the ultimatebranches and the lengths of ultimate shoots. Angles of insertionare measured as the angle formed by the main axis of thepenultimate stem and the upper (adaxial) side of the ultimatestem. Differences in insertion angles contribute significantly todifferent shapes for different branching systems. Overallbranch shapes vary from ovate (fig. 2B) to deltoid (fig. 4A) tonarrowly oblong (fig. 4F). The ovate type includes branchingsystems with ultimate shoots attached at angles of 45�–90� (fig.2B; fig. 4B, 4C). These systems look relatively open, and some-times the distal ends of ultimate shoots overlap each other (fig.4C, 4E). Deltoid branches have ultimate shoots attached atangles of 45�–50� (fig. 4A), and they appear to be more closedor slightly appressed, compared to ovate branches (cf. fig. 4A,4D). Narrowly oblong shoots have branching angles of45�–50� (fig. 4F). This is comparable to deltoid branches, butthe maximum length of the ultimate branches is shorter on

narrowly oblong shoots (i.e., 6–10 mm) than on deltoid shoots(i.e., 25–100 mm; fig. 4A–4F).

The length of ultimate branches varies considerably on asingle shoot system. Large ultimate shoots are typically locatedin the basal region, with small ultimate shoots positioned to-ward the apex and intermediate sizes intergrading between thetwo (figs. 2A, 4C). Basal ultimate branches range from 60 to150 mm long, whereas apical ultimate branches range from10 to 40 mm long. Ovate branching systems have the mostsimilarity in ultimate branch lengths, from the basal region tothe base of the apical region (fig. 2B), whereas in ovoid anddeltoid shoots, the width of ultimate branches ranges from 1.0to 2.3 mm long in the basal region to 0.7–1.8 mm long in theapical region.

Vegetative Leaves

Antepenultimate, penultimate, and ultimate leaves are hel-ically arranged, with a decurrent base, dentate margin, andmucronate apex with a curving tip (fig. 5A–5C; fig. 6A, 6B).The observed leaf size and shape depend on the order ofbranching represented by the specimen, on the mode and qual-ity of preservation, and on the angle of splitting of the rock.






Fig. 4 Thucydia gen. et sp. nov. General morphology of plagiotropic branching systems. A, Large system showing a penultimate shoot witha large number of ultimate shoots. Note that the deltoid overall shape is relatively long and narrow and the apex tapers to a point. Also notepenultimate leaves at the base (arrows). OUPH 13413 (G8) #0.6; cm. B, Middle zone of a plagiotropic branching system showingscale p 2.5alternate to subopposite attachment of ultimate shoots and different modes of preservation. The penultimate shoot is partially permineralized,as are the tips of two ultimate shoots (upper right). Coalified compressions and impressions of ultimate leaves are shown at the base (center)and tip (lower right) of some ultimate shoots. OUPH 13413 (GC-2) #0.4; cm. C, Broad plagiotropic branching system showingscale p 2relatively long ultimate branches. Ultimate branches are inserted at angles of 45� or greater. The shoot system looks open and the leaves looknarrow because the specimen is split through the center of the stems, revealing all leaves in a side view. OUPH 13415 (G1) #0.5; scale p 1cm. D, Section of partially permineralized plagiotropic branch. Branching system appears denser than specimen in fig. 6C because the ultimatebranches are inserted at angles of 45� or less, and because the specimen is preserved showing many leaves in face view. OUPH 13416 (G4) #1;

cm. E, Plagiotropic branching system consisting of a partially preserved penultimate stem with six ultimate shoots attached. Penultimatescale p 1stem is not fully in view, but it shows the attachment of the ultimate branches. Note leaves of penultimate shoot at arrows. Ultimate branchesare inserted at angles of 60�–75� and curve to extend from the axis at different angles. OUPH 13417 (G16) #0.5; cm. F, Smallscale p 1plagiotropic shoot with short ultimate branches. The penultimate stem is the narrowest, and the ultimate branches are the shortest among allthe specimens in the collection. Note that the penultimate and ultimate leaves are similar to those in fig. 6A and 6D. OUPH 13419 (GPC-1)#2; mm. G, Fragment of plagiotropic branching system displaying a single ultimate branch attached to the penultimate stem. Thescale p 3penultimate branch shows a mixture of leaves that are appressed to the stem and preserved in face view (small arrows), or diverging and preservedin side view (large arrows). Leaves on the penultimate and ultimate branches are very similar in shape but differ in size. Note that the leavesat the base of the ultimate branch (preserved in side view) appear quite different from those in the apical region (preserved in face view). OUPH13420 (G204) #1; cm.scale p 1

The most commonly observed leaves appear to be S shapedand are seen in side view because the branch has split throughthe center of the stem (figs. 2–4). Other leaves are exposed indifferent orientations, where they show wide variations inshape and size (figs. 2–4, 5A–5C). Leaves exposed in face viewappear to be appressed to the stem and are narrowly triangularto linear (figs. 4, 5A).

Antepenultimate leaves are wider than those on more distallevels of branching (table 1), with an incomplete width of1.0–1.5 mm. They are probably longer than leaves on thepenultimate and ultimate branches as well, but they are par-tially hidden (fig. 2A), and their observable lengths range from4.0 to 7.0 mm. However, their maximum length is not known.Leaves on penultimate shoots range from 5 to 12.5 mm longand from 1.0 to 1.5 mm wide in side view. Those exposed inface view are up to 3 mm wide (fig. 2A). They occur all alongpenultimate stems (fig. 4G) but are exposed best at the baseof the shoots (figs. 2A, 4A). Ranges of variation in the lengthof ultimate leaves from basal (3.0–6.0 mm) and apical regions(3.0–5.0 mm) are very similar. In side view, leaves range from0.4 to 0.5 mm in width, whereas in face view, they are up to1.0 mm wide.

Cuticular Characters

Cuticular features have been determined for penultimate andultimate leaves, in which they are the same. The adaxial surfaceof the leaf displays two bands of stomata that are separatedby a central stomatal free zone (fig. 5B; fig. 6B, 6C). Twostomatal free zones are also preserved at the margins of theleaf (fig. 5B; fig. 6B, 6C). Stomatal bands do not reach thevery base of the leaf (fig. 6C), and they join at the apex (fig.6D). Stomatal bands characteristically have a width of six toeight stomatal complexes that are interspersed with ordinaryepidermal cells (fig. 6B, 6C). Within a stomatal band, the sto-matal complexes are randomly arranged and longitudinallyoriented (fig. 6B, 6C). Individual stomatal complexes are cir-cular to elliptical, 20–26 mm long ( mm), and 15–21mean p 24mm wide ( mm), and they are composed of six tomean p 18

eight papillate subsidiary cells (fig. 6E–6H). Guard cells usuallyare not preserved (fig. 6G, 6H).

Subsidiary cells are oblong to semitriangular and 5–14( ) mm long, 6–14 ( ) mm wide at the base,mean p 9.5 mean p 9and 2–7 ( ) mm at the apex (fig. 6G). Some subsid-mean p 3.2iary cells are shared by adjacent stomata (fig. 6G). Papillaeare 5–10 mm long. They either overarch the position of theguard cells and seem curved, with a differentially thickenedtip (fig. 6H, 6I), or they are erect and linear (fig. 6D–6I).Papillae also occur on ordinary rectangular epidermal cells inthe stomatal free zones (fig. 6F). The papillae of subsidiarycells and ordinary epidermal cells are similar in size and shape(fig. 6F, 6H–6I), but their circular (in stomatal complexes) orlongitudinal (in epidermal cells) arrangement helps to identifythe stomata (fig. 6D–6F).

The abaxial surface of the leaf is characterized by ordinaryepidermal cells and interspersed trichome bases (fig. 6A). Noabaxial stomatal complexes have been found. Abaxial epider-mal cells display a variety of shapes, and depending on theirposition, they may be elongated, oblong, semitriangular, orrectangular (fig. 6A, 6K, 6L). Trichome bases are circular toelliptical (fig. 6K) and 5–11 mm in diameter. They are typicallyarranged in nearly parallel, transversely oriented rows andoccur over the entire abaxial surface of the leaf (fig. 6A, 6K,at arrows). However, many isolated trichome bases also occurbetween the rows (fig. 6L). Cell walls of trichome bases arethick, 0.7–1.3 mm ( mm), in comparison to the cellmean p 1walls of ordinary epidermal cells, which are 0.2–0.4 mm( mm; fig. 6L). Each trichome base is surroundedmean p 0.25by four to six thin-walled ordinary epidermal cells (fig. 6K,6L).

The dentate margins of the leaves have many teeth that areusually broken (fig. 6C, 6M, 6N). The margin has a thickercuticle than the rest of the leaf (fig. 6C, 6M), where the basesof the teeth appear darker with light microscopy than the ad-jacent epidermal cells (fig. 6M). Marginal teeth are linear andthin, with a broad base (fig. 6M, 6N) that ranges from 10 to




Fig. 5 Vegetative leaves of Thucydia gen. et sp. nov. A, Small plagiotropic shoot with two ultimate shoots attached, showing face view ofleaves. OUPH 13421 (GPC-1) #5; mm. B, Cuticular maceration of ultimate shoot showing leaves. Note that leaves are simple, linear,scale p 3and mucronate with recurved tip and decurrent base. Note also two bands of adaxial stomata (sb) separated by a stomatal free zone. OUPH13422 (M2019 u1) #30; mm. C, SEM of an ultimate shoot showing leaves. Note the S shape of leaves as well as mucronate tip,scale p 1dentate margin, abaxial trichomes, and adaxial papillae. OUPH 13423 (GW3) #20; mm. D, Oblique section of an ultimate leafscale p 1showing internal anatomy. Note leaf cuticle (cu), epidermis (ep), hypodermis (hy), mesophyll cells (me), vascular bundle (vb) surrounded by abundle sheath (bs), and trichome bases (tr). OUPH 13424 (M1451 a8) #40; mm. E, Ultimate leaf in cross section showing anatomicalscale p 0.5features of leaves. Note the shape of the leaf, spongy mesophyll (sm), and vascular bundle (vb). OUPH 13425 (M1454 f 3) #60; scale p

mm.0.25

60 mm wide and with a maximum observed length of 160 mm(fig. 6N).

Internal Anatomy

Stems of the penultimate and ultimate orders of branchinghave similar anatomical features and display both primary andsecondary tissues (fig. 7A, 7B). Primary tissues include a centralpith, eustele, and cortex (fig. 7A, 7B). The secondary bodyconsists of a bifacial vascular cambium, secondary xylem, sec-ondary phloem, and periderm (fig. 7B, 7D, 7I). The pith iscomposed of parenchyma cells with intercellular spaces andresin canals (fig. 7B, 7E, 7F). Pith parenchyma cells are thinwalled and circular in cross section (fig. 7B, 7F), ranging from20 to 64 mm ( mm) in diameter. In longitudinalmean p 44.35sections, they are rectangular, arranged in vertical files (fig.7C–7E), and 17–49 mm ( mm) long. Resin canalsmean p 33.5are circular to oval in cross section (fig. 7B, 7F), and most arelocated toward the periphery of the pith (fig. 7B). They extendlongitudinally through the stem (fig. 7E), and each has a dis-tinct epithelial lining and dark internal contents (fig. 7E, 7F).The periclinal walls of the epithelial cells are much more prom-inent than the anticlinal walls, and the epithelial layer usuallyappears as a narrow ring around the dark internal contents.

However, by carefully focusing up and down on the surfaceof a section, one can identify anticlinal cell walls. In crosssection, resin canals are 40–90 mm ( mm) in di-mean p 61.2ameter, and the epithelial lining is 2–5 ( ) mm wide.mean p 2.5The pith is surrounded by a eustele of tiny primary bundles(fig. 7B). Tracheids of primary xylem have helical thickeningson the secondary walls (fig. 7G). In cross section, tracheidsare 9–17 mm ( mm) in diameter (fig. 7J).mean p 10.9

The secondary body of the plant is characterized by a prom-inent zone of wood (fig. 7A, 7B, 7H, 7J), secondary phloem,and periderm (fig. 7A, 7B, 7I, 7N). A bifacial vascular cam-bium is located between the secondary xylem and secondaryphloem (fig. 7I, 7N), but cells are rarely preserved (fig. 7N).The secondary xylem is composed of radially elongated col-umns of tracheids and ray parenchyma cells (fig. 7I, 7J). Col-umns are 13–26 cells long. In cross section, the tracheids arerectangular to circular with thick walls (fig. 7J) and 14–44 mm( mm) in diameter. They have uniseriate borderedmean p 24.5pits on the radial walls (fig. 7K). Wood rays are composed ofparenchyma cells that are rectangular in cross section (fig. 7J).Individual rays are homocellular and uniseriate with smoothcross walls (fig. 7L), and they are one to nine cells high (fig.7L, 7M). In cross section, ray cells range from 6 to 29 mm



Fig. 6 Thucydia gen. et sp. nov. Cuticular features of vegetative leaves. A, Abaxial cuticle of ultimate leaf showing trichome bases (tr) fromthe adaxial side of the leaf. Note that trichome bases are distributed across the abaxial surface in almost horizontal parallel rows that areperpendicular to the main axis of the leaf. OUPH 13426 (M2019 u1) #58; mm. B, Adaxial surface of an ultimate leaf. Note twoscale p 1stomatal bands (sb), each with a breadth of four to six stomata, and note that these bands are separated by a stomatal free zone (sf) in themiddle region of the leaf. There are also two stomatal free zones at the leaf margins. Also note that the leaf is curved at the tip and partiallyfolded at the base (arrow). OUPH 13427 (M2006) #24; mm. C, Adaxial surface of an ultimate leaf showing broken teeth on thescale p 0.25margin (at left) and two stomatal bands (sb). Note that the stomatal bands do not reach the base of the leaf. OUPH 13427 (M2006) #33;

mm. D, SEM of the adaxial surface of an ultimate leaf showing the apical region where the two stomatal bands are fused. Notescale p 0.25that the apex is characterized by many papillae (pa). The pointed tip of this leaf is absent. OUPH 13428 (G3A3) #400; mm. E,scale p 50SEM of adaxial surface of an ultimate leaf. Note that stomatal bands (sb) are distinguished by overarching papillae of subsidiary cells (arrows).OUPH 13429 (G1A3) #320; mm. F, SEM of the adaxial surface of ultimate leaf showing papillae on epidermal cells (ip) and subsidiaryscale p 50cells (op). OUPH 13429 (G1A3) #470; mm. G, DIC of stomatal band showing haplocheilic stomata (large arrows). Note the numberscale p 25of subsidiary cells per stoma and erect papillae (small arrows). Also note erect papillae on top of subsidiary cells. OUPH 13430 (Glu-1) #440;

mm. H, SEM of adaxial stomatal complex showing six subsidiary cells with overarching papillae (arrows). Note that no guard cellsscale p 25are preserved. OUPH 13429 (G1A3) #500; mm. I, SEM of adaxial surface of ultimate leaf showing papillae. OUPH 13431 (G3B2)scale p 10#800; mm. J, SEM of abaxial surface of ultimate leaf showing dentate margin (at right) and trichome bases (arrows). Note arrangementscale p 20and shape of trichome bases. Also note two saccate pollen grains. OUPH 13432 (GE5) #120; mm. K, Abaxial surface of ultimatescale p 50leaf showing trichome bases. Note that trichome bases are arranged in almost parallel rows (follow arrows). OUPH 13427 (M2006) #35;

mm. L, Abaxial surface of ultimate leaf showing trichome bases. Note the central ring at the base of the trichome and elongatedscale p 20ordinary epidermal cells. OUPH 13426 (M2019 u1) #83; mm. M, Dentate margin of an ultimate leaf. Note the thickening of epidermisscale p 10at the teeth, the broad base, and narrow distal end that is often broken. OUPH 13427 (M2006) #33; mm. N, SEM of ultimate leafscale p 10margin. Note the adaxial surface with trichome bases, long and narrow ends of teeth, and dispersed pollen grains. OUPH 13429 (G2A3) #330;

mm.scale p 50






Fig. 7 Thucydia gen. et sp. nov. Internal anatomy of the vegetative shoots. A, Cross section of permineralized ultimate shoot showing internalanatomy of stem and leaves and helical phyllotaxy. Note that the stem has a large pith (pi) that is surrounded by secondary xylem (sx) andbark (br). Also note mesophyll cells (me) and vascular bundle (vb) in leaves. OUPH 13437 (M1454 f17) #49; mm. B, Cross sectionscale p 260of a penultimate shoot showing internal anatomy of the stem. The pith (pi) has two cellular components (pith parenchyma and resin canals)and is surrounded by a eustele, secondary phloem (sp), and secondary xylem (sx). Also note position of primary xylem (px) and periderm (pe).OUPH 13438 (M2019 b10) #30; mm. C, Penultimate shoot in longitudinal section showing leaves (left) and pith (center). Notescale p 200insertion of leaves (l), parenchyma cells (pc), and resin canals (rc) in the pith. OUPH 13439 (M2019 c1) #11; mm. D, Longitudinalscale p 500section of penultimate shoot showing periderm (pe), pith, and radial section of the secondary xylem (right) with tracheids (tr) and wood rays(wr). OUPH 13440 (M2019 c2) #17.5; mm. E, Longitudinal section of penultimate shoot showing three longitudinally orientedscale p 250resin canals. Note the epithelial lining (el) and resinous appearing contents. OUPH 13441 (M2019 a3) #83; mm. F, Penultimatescale p 40shoot in cross section showing histology of pith region. Note the size and arrangement of resin canals (rc) and parenchyma cells. Also note theepithelial lining (el) of resin canals and dark contents. OUPH 13442 (M2019 b3) #110; mm. G, Longitudinal section of penultimatescale p 2.5shoot showing pith (left) and primary xylem (px). Note that the tracheids have helical thickenings on the secondary walls (small arrows). Alsonote the contact between tracheids (large arrows). OUPH 13441 (M2019 a3) #57.5; scale 20 mm. H, Longitudinal section of penultimate shootshowing two branches (at arrows). Note the small pith and the large amount of secondary xylem on both branch traces. OUPH 13443 (M2019c4) #19; mm. I, Penultimate shoot in cross section showing secondary growth of stem. Note secondary xylem (sx), vascular cambiumscale p 500zone (vc), secondary phloem (sp), periderm (pe), and leaf (l). Note that secondary phloem and inner layers of the periderm are not often preserved.OUPH 13444 (M2019 b4) #23; mm. J, Cross section of ultimate shoot showing primary xylem (px) and secondary xylem (sx).scale p 500Note the parallel rows of tracheids and wood rays (wr). OUPH 13445 (M2027 b1) #13; mm. K, Penultimate shoot in radial sectionscale p 100showing secondary xylem and rays (wr). Note uniseriate circular bordered pits (p) in tracheids and rays (wr) that are one to three cells in height.OUPH 13440 (M2019 c2) #79; mm. L, Tangential section of penultimate shoot showing secondary xylem. Note uniseriate woodscale p 50rays that are one to nine cells in height. OUPH 13446 (M2019 c3) #82; mm. M, Tangential section of penultimate shoot showingscale p 50unicellular uniseriate wood rays (arrows). OUPH 13446 (M2019 c3) #103; mm. N, Cross section of penultimate shoot showing thescale p 25secondary xylem (sx), vascular cambium zone (vc), secondary phloem (sp), and periderm (pe). Note that the cambial zone and phloem appeardistinct from secondary xylem and periderm. OUPH 13444 (M2019 b4) #69; mm. O, Cross section of penultimate shoot showingscale p 250periderm. Note the arrangement and shape of the phellogen cells (ph) and remnants of cork cells (cc). OUPH 13444 (M2019 b4) #121;

mm.scale p 100

( mm) in diameter and are 17–29 mm (mean p 13.1 mean pmm) high in radial section. The secondary phloem is rep-23.9

resented by sieve cells and sclereids (fig. 7N). In cross section,the sieve cells are thin walled, rectangular, and 8–31 mm( mm) in diameter (fig. 7N). Sclereids are thickmean p 15.2walled, circular to oval in shape (fig. 7N), and 12–35 mm( mm) in cross section. In longitudinal section, theymean p 21are rectangular and 17–29 mm ( mm) high.mean p 23.4

Periderm is composed of phellogen and cork cells (fig.7A–7C, 7I). It is usually preserved as a dark layer that sur-rounds the secondary phloem (fig. 7B) and is often easy toidentify because of the nonpreservation of secondary phloemin many parts of the stem (fig. 7I, 7N). The phellogen is com-posed of large, thin-walled cells that are rectangular in crosssection (fig. 7N, 7O), 23–58 mm ( mm) in di-mean p 38.2ameter, and 20–70 mm ( mm) high in longitudinalmean p 47section. Phellem is several layers thick (fig. 7O). Cork cells arethin walled and rectangular and have almost the same dimen-sions as the phellogen cells (fig. 7O).

Anatomically preserved leaves are usually exposed inoblique and cross section, where their shape ranges fromwidely rhomboidal to narrowly transversely rhombic (fig. 5D,5E; fig. 7A). Ultimate leaves are characterized by a thick cuticleon both surfaces, with numerous trichome bases on the adaxialsurface (fig. 5D). Below the cuticle, a single layer of epidermalcells is preserved (fig. 5D). The epidermis is composed of thin-walled rectangular cells that are 6–15 mm ( mm)mean p 10.7long and 4–8 mm ( mm) wide in cross section (fig.mean p 4.65D). A one- or two-layered hypodermis is preserved beneaththe epidermis (fig. 5D). In cross section, hypodermal cells arethick walled, oblong to circular, and 9–15 mm (mean p 16.4mm) long and 9–29 mm ( mm) wide (fig. 5D). Themean p 17.1

mesophyll of the leaf is composed of incompletely preservedthin-walled parenchyma cells that sometimes display dark con-tents and that in oblique section appear as large polyhedriccells with plicate walls (fig. 5D). In cross section, these cellsare round to angular (fig. 5D). Mesophyll cells are 17–41 mm( mm) long and 15–61 mm ( mm)mean p 29.6 mean p 29.7wide. A bundle sheath surrounds the single vascular bundleof the leaf (fig. 5D). The bundle sheath is composed of onelayer of large, thick-walled polyhedral cells that sometimeshave dark contents (fig. 5D). Bundle sheath cells are 18–41mm ( mm) long and 17–38 mm ( mm)mean p 26.5 mean p 25.5wide. The vascular bundle is represented by xylem (fig. 5D,5E), consisting of tracheids that are 9–20 mm ( mm)mean p 12long and 6–17 mm ( mm) wide.mean p 10.6

Pollen Cone

The pollen cone is represented by both part and counterpartof a single specimen and provides the first unequivocal evidencefor compound pollen cones in conifers (Hernandez-Castillo etal. 2001). On the rock surface, this cone is superficially similarto an ultimate vegetative shoot (fig. 8A), but closer exami-nation reveals that it comprises bracts that partially cover pol-len sacs and sterile scales (fig. 8B–8G). The cone is 8.2 cmlong and 0.9 mm wide. Bracts are simple, linear, and incurved,with a dentate margin and mucronate tip (fig. 8B–8F). Bractshave a decurrent base (fig. 8D, at arrowhead) subtending theaxillary fertile shoot (fig. 8C, at arrowheads). Bracts are3.0–5.0 mm ( mm) long, 1.0–2.0 mm (mean p 4 mean p 1.4mm) wide, and 0.2–0.6 mm ( mm) thick. The ax-mean p 0.4illary fertile shoots (fig. 8C, at arrowheads) bear both sterilescales and pollen sacs (fig. 8C–8G). Sterile scales are consis-



1168

Fig. 8 Thucydia gen. et sp. nov. compound pollen cone. A, Surface view of compression showing general morphology. Note that the overallappearance is very similar to that of a vegetative ultimate shoot. OUPH 13457 (G82) #3; cm. B, Enlargement of A, showing largescale p 1bracts (b) and pollen sacs (ps). OUPH 13457 (GR82) #6; cm. C, Incomplete chemical maceration of pollen cone showing largescale p 0.25bracts (b), axillary fertile shoot (arrow head), and five sterile scales (bracket). Note difference between bracts and sterile scales. OUPH 13458(G82) #8; mm. D, Chemical maceration of pollen cone showing cone axis (ca), bracts (b), sterile scales (sc), and erect pollen sacsscale p 2.5(ps). Note that each node has a bract and shows erect pollen sacs, and the basal node also shows two sterile scales between the decurrent base(at arrow head) of the bract and pollen sacs. OUPH 13458 (G82) #6; mm. E, SEM of pollen cone showing bracts (b) and erectscale p 2pollen sacs (ps). OUPH 13460 (G82-glll5) #20; mm. F, SEM showing incomplete bract (b), sterile scales (sc), and bent-back pollenscale p 1sacs (ps). Note that sterile scales are located between the bract and pollen sacs. OUPH 13461 (G82-gll7) #29; mm. G, SEM of adaxialscale p 1surface of bract (b) showing decurrent base that encloses several sterile scales (sc) and two pollen sacs (ps). OUPH 13460 (G82-g13) #50;

mm.scale p 500



Fig. 9 Thucydia gen. et sp. nov. Cuticular features and morphology of pollen sacs and pollen grains. A, Enlargement of fig. 8G, showingbract base (b) with sterile scales (sc) and two pollen sacs (ps). Note that the pollen sacs are located on top of sterile scales, and two saccatepollen grains are preserved in the interior of the pollen sac. OUPH 13460 (G82-gzz12) #100; mm. B, SEM of the adaxial surfacescale p 200of the bract showing papillate surface. Note that rings of papillae delimit stomatal complexes (arrows). OUPH 13460 (G82-gzz4) #575;

mm. C, SEM of the apical region of sterile scale contrasting cuticular features of abaxial (at left) and adaxial surfaces (at right). Notescale p 50that the abaxial surface is smooth and the adaxial surface is covered by stomata with erect papillae (white arrows). OUPH 13461 (G82-gzz3)#350; mm. D, Chemical maceration of pollen cone showing isolated erect pollen sac and sterile scale. Note position and the ellipticalscale p 50shape of pollen sac and leaflike shape of sterile scale. Also note the basal stalk of pollen sac (arrow). OUPH 13462 (G82-pcp-6) #50;

mm. E, SEM of pollen sac wall showing outer cellular layer and inner noncellular layer. Note the angular cells in the outer layerscale p 200(arrow) and the surface of the inner layer. OUPH 13461 (G82-gzz44) #700; mm. F, Chemical maceration of pollen sac showingscale p 50pollen sac wall (arrow) and saccate pollen grains. Note that the pollen grains are tightly packed. OUPH 13463 (G82-pcp-5) #56; scale p

mm. G, SEM of pollen sac interior showing three saccate pollen grains (arrows) that are surrounded by a thin membranous substance.250OUPH 13464 (G82-gzz34) #300; mm. H, Potonieisporites prepollen grain attached to a fragment of pollen sac wall (white arrow).scale p 100Note the saccus (s) that surrounds a central body. Also note monolete suture (arrow head) and parallel folds on central body. OUPH 13465(G82-pcp-4) #480; mm. I, SEM of Potonieisporites prepollen grain showing saccus (s) and central body (cb) with monolete slit.scale p 25OUPH 13464 (G82-gll6d) #700; mm.scale p 25






Fig. 10 Thucydia gen. et sp. nov. Ovulate fertile structures. A, Penultimate shoot showing ovulate fertile zone. Note that vegetative leavesend at the base of the ovulate fertile zone (white arrow) and appear again at the distal end of the ovulate fertile zone (black arrow). OUPH13447 (GR11) #2; cm. B, Antepenultimate shoot bearing a penultimate shoot with ovulate fertile zone. Note the attachment ofscale p 1penultimate shoot (black arrow) and fertile zone (between white arrows) among basal and distal vegetative regions. OUPH 13448 (GR8) #1.3;

cm. C, Incomplete chemical maceration of an ultimate shoot showing the transition from the fertile zone (black bracket) to the apicalscale p 1vegetative zone (white bracket). Note the size of the bracts (b) and vegetative leaves (vl). Also note fragments of axillary fertile shoots in theaxil of bracts (e.g., white arrow). OUPH 13449 (GR14) #3; cm. D, Fragment of a fertile plagiotropic branching system (holotype)scale p 1showing the antepenultimate shoot (black arrow) and three penultimate shoots, two of which are attached in this view. Attached penultimateshoots bear broken ovulate fertile zones (white arrows). Note size of leaves on both branching orders. OUPH 13450 (GR1) #2; cm.scale p 1E, Isolated ovulate fertile zone showing general morphology. Note that the base of the fertile zone lacks leaves, but leaf scars are present(arrowheads). The ovulate fertile zone is represented by a main axis (between arrowheads) that bears nodes with bracts and axillary fertileshoots (black arrows). Also note two vegetative leaves at the apex of the fertile zone (white arrows) and a detached ovuliferous dwarf shootpreserved near the base (bracket). OUPH 13451 (GR17) #2; cm.scale p 1

tently positioned between the bract and the pollen sacs (fig.8D–8G). They are simple, linear, 0.6–1.1 mm (mean p 0.9mm) long, 0.2–0.4 mm ( mm) wide, and 0.2 mmmean p 0.3thick, with a curved mucronate apex (fig. 8C, 8D) and dentatemargins (figs. 8G, 9A). The number of sterile scales per axillaryshoot ranges from five to eight (fig. 8C, 8G). Both bracts andsterile scales display the same cuticular features. The entireadaxial surface bears stomatal complexes and ordinary epi-dermal cells that are covered by papillae (fig. 8G). Papillae aretypically erect, but sometimes those of the subsidiary cellsslightly overarch the position of the guard cells to help delimitthe stomatal complexes (fig. 9A–9C). Stomatal complexes arecomposed of four to eight subsidiary cells. The abaxial surfaceof bracts and sterile scales is nonpapillate (figs. 8E, 9C) andcovered by regularly arranged trichome bases and interspersedordinary epidermal cells (fig. 9C).

As can be seen with both light microscopy and SEM, pollensacs are consistently positioned between the main axis of thecone and the sterile scales (figs. 8D–8G, 9A). The number ofpollen sacs per axillary shoot ranges from three to four (fig.8E). Pollen sacs are always covered by the bract (fig. 8B,8D–8F), and their tips reach to the bract midlevel (fig. 8E).Pollen sacs are ellipsoidal (figs. 8D, 9D), with a rounded apex(figs. 8E, 9D) and a small stalk at the base (fig. 9D, at arrow).They measure 0.8–1.2 mm long, with a maximum diameterof 0.3–0.6 mm. The pollen sac wall is composed of two layers(fig. 9E). The outer layer consists of angular cells that are28–42 ( mm) mm long and 8.3–14 (mean p 36.3 mean p

mm) mm wide (fig. 9E). The inner layer is noncellular11.58(fig. 9E) and covers tightly packed, saccate pollen grains (fig.9F, 9G). Pollen grains are elliptical to circular in polar views(fig. 9G, 9H), with a maximum diameter of 62–130( mm) mm. They are monosaccate with a centralmean p 92.3body that has a pair of parallel folds and a monolete suture(fig. 9H, 9I), and if found dispersed, these pollen grains wouldbe assignable to the sporae dispersae genus PotonieisporitesBharadwaj (Bharadwaj 1964).

Ovulate Fructifications

The ovulate structures of T. mahoningensis consist of com-pound fertile zones that are located on leafy shoots and thatoccur between more proximal and more distal vegetativeregions (fig. 10A–10E). The maximum observed length of anovulate fertile branch is 11 cm, and it is more or less evenly

divided between the proximal vegetative region, the fertilezone, and the distal vegetative region (fig. 10A). Most of theovulate branches are broken near the tip of the fertile zone,but at least a few vegetative leaves usually are present at thedistalmost level preserved (fig. 10C–10E).

One specimen displays ovulate shoots attached to a leafybranch (fig. 10D), showing that fertile shoots are grouped onmore proximal branches (fig. 10D). The stem of the proximalleafy branch is considerably wider (5–8 mm) than are the stemsof the fertile shoots (i.e., 0.15–0.25 mm). It is hard to tell forcertain, but the ovulate shoots appear to be diverging on morethan two radii, indicating that the proximal leafy branch is anorthotropic stem. Leaves on the proximal leafy branch (orstem?) are bigger than the leaves of fertile shoots (fig. 10D),measuring 14–17 mm ( mm) long, 2.8–3.0 mmmean p 16( mm) wide, and 0.8–1.1 ( mm) thick.mean p 3 mean p 1.0Leaves in the proximal vegetative region of fertile shoots arelarger than those in the distal vegetative region (fig. 10A, 10B).Proximal leaves are 5–10 mm ( mm) long, 1.0–1.2mean p 8mm ( mm) wide, and 0.5–1.0 mm (mean p 1 mean p 0.75mm) thick, whereas distal leaves are 3–6 mm ( mm)mean p 4long, 0.8–1.0 mm ( mm) wide, and 0.4–0.6 mmmean p 0.9( mm) thick.mean p 0.5

Fertile zones range from 3.0 to 4.5 cm in length and 0.9 to1.5 cm in width and consist of helically arranged bracts (fig.10C, 10E) with axillary ovuliferous dwarf shoots (fig. 10C,10E; fig. 11A–11E). Bracts are quite similar to those of thepollen cones, being linear and gently incurved, with a mucro-nate tip (fig. 10C; fig. 11B; fig. 13A, 13C). Ovulate bracts arelarger than vegetative leaves on the rest of the shoot (fig.10A–10C), measuring 8–11 mm ( mm) long,mean p 101.0–1.5 mm ( mm) wide, and 0.5–1.2 mmmean p 1.2( mm) thick. Cuticular features of bracts differmean p 1.0from those of vegetative leaves by having an adaxial surfacethat is entirely covered by evenly distributed stomatal com-plexes (fig. 13C), and in this respect, the ovulate and pollencone bracts are comparable (table 1). Both ordinary epidermalcells and subsidiary cells display prominent papillae (fig. 13C),most of which are erect (fig. 13C, 13D). Stomatal complexesare composed of four to six subsidiary cells (fig. 13D). Theabaxial surface of the ovulate bracts displays rectangular epi-dermal cells and trichome bases (fig. 13E).

Organization of the ovuliferous dwarf shoots has been ob-served in several intact fertile zones (fig. 10A, 10D, 10E) and




also in isolated specimens, in which the overall morphologyis easiest to interpret because it is not obscured by other struc-tures (fig. 10E; fig. 11A, 11B; fig. 13B). Individual ovuliferousdwarf shoots are fan shaped (fig. 11A, 11C, 11D), with anarrow axis basally, several sterile scales diverging from allsides, and three or four sporophylls distally (fig. 11A, 11C,11D; fig. 13B). Ovuliferous dwarf shoots range from 8 to 9mm in length. They are 1.2–3 mm wide at the base, fanningoutward to 6–7.5 mm at the apex. Sterile scales are linear witha curved mucronate tip (figs. 11A, 11C, 11D, 13F). The num-ber of sterile scales per axillary fertile shoot ranges from 10to 15. Sterile scales are 2–5 mm ( mm) long, 0.3–0.6mean p 3mm ( mm) wide, and 0.3–0.5 mm (mean p 0.5 mean p 0.4mm) thick. They display the same cuticular pattern as thebracts, in which the adaxial epidermal cells are papillate (fig.13F) and ordinary epidermal cells of the abaxial surface aresmooth and interspersed with trichome bases (fig. 13F, atarrow).

Sporophylls extend from the apex of the ovuliferous dwarfshoots (fig. 11A–11E), spreading distally in a single plane andseparating from each other laterally (figs. 11A–11D,12A–12C). They are linear (fig. 11A–11D) with a recurved tip(figs. 11B, 13G) and are covered on all sides by small papillaethat are 12–15 mm ( mm) long. There is a singlemean p 13.5seed scar at the recurved apex (fig. 13G) that points towardthe base of the sporophyll. Sporophylls are 3–4 mm( mm) long and 1–1.5 mm ( mm ) wide.mean p 3.2 mean p 1.3Seeds are elliptical to oval (fig. 11E, 11F; fig. 13H) and ca. 2mm long and 1 mm wide, with a narrow peripheral wing (fig.11E, 11F, at arrows; fig. 13H).

Discussion

Taxonomic Distinctiveness and Systematic Placementof Thucydia mahoningensis

Thucydia mahoningensis displays a novel combination ofcharacters that falls outside the circumscription of currentlyrecognized conifer families. Thucydia is a biological taxon offossils (Greuter et al. 2000) consisting of plants that are smalltrees with an orthotropic stem and plagiotropic penultimatebranches that typically bear two ranks of ultimate shoots ina regular, pinnate arrangement. Leaves vary in size on differentorders of branching but are simple and helically arrangedthroughout the plant. Stems are eustelic, with tiny endarchcauline bundles and dense wood, and they produce peridermon all branch orders. The pith is parenchymatous and containsresin canals that have an epithelial lining. Stomata of the veg-etative leaves occur in two adaxial bands, but bracts and sterilescales have stomata across the entire adaxial surface. Stomataare absent from the abaxial surface of all leaf types. Individualstomatal complexes are randomly arranged within the bandsand are characterized by a ring of four to eight papillate sub-sidiary cells, depending upon the type of leaf (table 1).

Plants have terminal pollen cones and compact ovulate fer-tile zones that occur between vegetative regions on lateralbranches. Both ovulate zones and pollen cones are compoundshoot systems that consist of a primary axis that bears helicallyarranged bracts with axillary dwarf shoots. Polliniferous dwarfshoots are bilateral, with five to eight sterile scales and three

to four sporophylls that each bear an erect terminal pollen sac.Sterile scales are positioned adjacent to the bract and laterally,whereas microsporophylls occur only on the side of the dwarfshoot that faces the primary cone axis. Grains are oval eu-saccate prepollen, with the monosaccus inflated in the equa-torial plane. A bent monolete suture is positioned parallel tothe long axis on the proximal surface of the grain and is per-pendicular to two crescent-shaped folds of the corpus. Ovu-liferous dwarf shoots are also bilateral, with 10–15 sterilescales around all sides of the axis and three to four narrowsporophylls that fan outward from the dwarf shoot apex in asingle plane. Sporophylls all recurve in the same direction,positioning the ovules between the ovuliferous dwarf shootand the primary axis of the fertile zone. Ovules are apical andinverted, flattened and oval, and display a symmetrical narrowwing around the major plane.

Diagnostic characters of the Thucydiaceae comprise thecombination of compound ovuliferous fertile zones, compoundpollen cones, and a number of unique anatomical and cuticularfeatures. Compound pollen cones have not been documentedamong previously described Paleozoic conifer species (Mapesand Rothwell 1998; Rothwell and Mapes 2001), and micro-sporangiate dwarf shoots are otherwise unknown among con-ifers as a whole (Hernandez-Castillo et al. 2001). Ovuliferousfructifications that consist of fertile zones rather than terminalcones are uncommon for conifers (table 4). Other than tera-tologies found in both living and fossil species (Chamberlain1935; Florin 1938–1945), ovuliferous fertile zones are knownonly for T. mahoningensis and the Permian species Concho-lepis harrisii Meyen (Rothwell and Mapes 2001) and Voltziahexagona (Bischoff) Geinitz (Schweitzer 1996; table 4).

Thucydia mahoningensis is the first walchian species to dis-play resin canals with an epithelial lining. Moreover, T. ma-honingensis is the first walchian conifer for which the stomataldistribution pattern on fertile leaves is different from that onvegetative leaves. Several other systematically informativecharacters of Thucydia are also found in previously describedPaleozoic conifers and conifer-like plants, but these do notoccur in the combination that characterizes Thucydia (tables2–4; Rothwell and Mapes 2001). Commonly shared charactersof walchian conifers include plant architecture and branchingpattern, helically arranged leaves, eustelic stem anatomy withdense wood, monolete prepollen grains that are monosaccate,bilateral ovuliferous dwarf shoots that have several sterilescales and easily recognizable apical megasporophylls with in-verted ovules, and oval ovules with a narrow peripheral wing(tables 2–4).

Comparisons of Thucydia to PreviouslyDescribed Walchian Conifers

Branching patterns and plant architecture. As early as1927, Florin (1927) recognized that walchian conifers are typ-ically small trees with an orthotropic stem and with plagio-tropic laterals that typically have two orders of branching.Pollen cones terminate ultimate lateral branches. Ovulatecones also terminate branches (Florin 1938–1945), except inT. mahoningensis, in which ovulate fertile zones occur in themidregion of lateral branches. Orthotropic stems are repre-sented by the morphogenera Tylodendron Weiss and Endolepis




Fig. 11 Thucydia gen. et sp. nov. Ovulate fertile zones, dwarf shoots, and seeds. A, Partially macerated ovulate fertile zone showing twoaxillary fertile shoots. Note shape and position of dwarf shoot (Ds), sporophylls (S), and sterile scales (sc). OUPH 13454 (GR-15) #4;

mm. B, Middle region of an ovulate fertile zone showing arrangement of axillary dwarf shoots (Ds). Note the arrangement of bractsscale p 5(B), sporophylls (S), and sterile scales (sc). Note also that bracts and sterile scales have pointed apices, whereas sporophyll tips are rounded.OUPH 13453 (GR-13) #4.4; mm. C, Detached axillary dwarf shoot showing the adaxial surface. Note that the shoot terminates asscale p 5four free sporophylls (S). The bases of two sporophylls are indicated by arrowheads, and sterile scales (sc) are preserved at both sides of theshoot. OUPH 13451 (GR-17) #4.8; mm. D, Counterpart of C; image inverted vertically to correspond with C. Note the sporophyllsscale p 5(S) at the apex of the shoot and sterile scales (sc) that are located at the sides of the axillary dwarf shoot. Bases of sporophylls are identifiedby arrowheads. OUPH 13452 (GR-7) #4; mm. E, Base of sterile shoot (left) and an ovulate fertile zone (right) showing ultimatescale p 5leaves (holotype), one axillary dwarf shoot (Ds) with sporophylls (S), and four almost complete oval seeds with a peripheral wing (w). OUPH13450 (GR-1) #3.5; mm. F, Detached seeds from one ovulate fertile zone of specimen figured in E. Note that seeds are elliptical toscale p 5oval in shape with a narrow peripheral wing (w). OUPH 13450 (GR-1) #6; mm.scale p 2

Schleiden and by a few orthotropic leafy shoots with attachedlateral branches. The best examples of the latter are assignedto Lebachia piniformis (Taf. 9–10, Abb. 14 and Taf. 13–14,Abb. 5 of Florin 1938–1945; pUtrechtia floriniformis Mapesand Rothwell) and T. mahoningensis (figs. 2A, 3); both con-form to Florin’s interpretation that the plants were similar inappearance to living species of Araucaria (Florin 1938–1945,1951).

Most walchian conifers display plagiotropic lateral branchsystems (Florin 1938–1945; Clement-Westerhof 1984; Mapesand Rothwell 1988; Kerp et al. 1990; Rothwell et al. 1997)that indicate a common overall plant architecture. Other spe-cies have laterals that branch in three dimensions. The latterinclude species of Lecrosia Florin, Palaeotaxites praecursorWhite, species of Paranocladus Florin, and some specimensthat occur near Garnett, Kansas (e.g., pl. 3, fig. 6, of Rothwell




Fig. 12 Thucydia gen. et sp. nov. Digitized tracings of ovuliferousstructures; sporophylls identified by numbers and sterile scales labeledwith letters. A, Side view of two ovuliferous dwarf shoots in axils ofbracts (B) shown in fig. 11B. Note shape of dwarf shoots, divergenceof sterile scales (letters), and orientation of sporophylls (numbers).Note also that more than one sporophyll is difficult to identify in thisview. B, Part and counterpart of ovuliferous dwarf shoot in fig. 11Cand 11D, oriented in face view. Note sterile scales (letters) and spo-rophylls (numbers). C, Recurved sporophyll tip in fig. 13G showingposition of scar (sc) from which inverted ovule has been detached.

et al. 1997). The ongoing analysis of growth architecture forT. mahoningensis and other walchian species will provide moredetailed information to help clarify the growth forms and lifehistory patterns of these Paleozoic conifers.

Vegetative leaves. Patterns of leaf morphology vary amongPaleozoic conifers. Some walchian species, including T. ma-honingensis, Ernestiodendron filiciforme (Schlotheim) Florin,and Lecrosia grand’euryi Florin (table 2), have simple vege-tative leaves throughout the plant (Florin 1950). Other (non-

walchian) Paleozoic conifers also show this pattern (i.e., C.harrisii Meyen, Dolmitia cittertiae Clement-Westerhof, Fer-ugliocladus patigonicus [Feruglio] Archangelsky and Cuneo,Ferugliocladus riojanum Archangelsky and Cuneo, Kunguro-dendron sharovii Meyen, Majonica alpina Clement-Westerhof,Ortiseia leonardii Florin, O. junkeri Clement-Westerhof, Or-tiseia visscheri Clement-Westerhof, Timanostrobus muravieviiMeyen, Ugartecladus genoensis Archangelsky and Cuneo, Ull-mannia frumentaria [Schlotheim] Goeppert, V. hexagona [Bi-schoff] Geinitz, and Voltzia liebeana sensu Schweitzer [1996];table 2), but as discussed below, these voltzialeans from An-gara, Gondwana, and Late Permian deposits in Euramericahave ovulate cones that are distinctively different from theovulate fertile zones of T. mahoningensis and the cones of otherwalchian species (table 4).

Some walchian conifers display position-related hetero-phylly. Those species bear simple leaves on ultimate branchesand forked leaves on both penultimate branches and the mainaxis of ovulate cones. That pattern occurs in Emporia lockardii(Mapes and Rothwell 1991) and three unnamed Upper Penn-sylvanian species from Hamilton, Kansas (Liu et al. 2000),Lecrosia gouldii Florin, Lebachia speciosa, and Walchia (Le-bachia?) schlotheimii Florin. Other species, such as E. filici-forme, Lebachia garnettensis, Lebachia laxifolia, Lebachiafrondosa, Lebachia hypnoides, Walchia (Ernestodendron?)arnhardtii, and Walchia (Ernestodendron?) germanica Florin,have simple vegetative leaves, but the ovulate cone bracts areforked (Florin 1938–1945; Winston 1984).

Some species, including U. floriniformis (pL. piniformis),are described as having simple and forked leaves intermixedon penultimate stems (Florin 1938–1945, 1950, 1951). How-ever, our recent reinvestigation of several hundred specimenspreviously studied and described by Florin (1938–1945) aswell as our study of numerous additional specimens revealedno unambiguous examples of that pattern. Most of the spec-imens are not well enough preserved to display unequivocalleaf morphology on the penultimate stems, but others eitherclearly have simple leaves or show a combination of forkedleaves and broken or partly buried leaves on the penultimateaxis. We suspect that some of the broken or only partly buriedpenultimate leaves have been interpreted as simple by previousauthors. The distribution of simple and forked leaves on thepenultimate shoot systems of European walchian conifers is inneed of systematic reexamination and clarification.

Anatomical characters. The anatomy of T. mahoningensisis generally similar to the few other Paleozoic conifers forwhich internal cellular structure is known. Stems of T. ma-honingensis display a relatively large parenchymatous pith,like E. lockardii (Mapes and Rothwell 1984), Szecladia mul-tinervia Yao et al. (Yao et al. 2000), and unnamed walchianspecimens from Middle Pennsylvanian sediments of Oklahoma(Rothwell 1982) and Upper Pennsylvanian deposits of Kansas(Mapes and Rothwell 1988; Rothwell et al. 1997). Some Pa-leozoic conifers have resin rodlets (E. lockardii; Mapes andRothwell 1984), sclereids (S. multinervia Yao et al. 2000),sclerotic nests, or no secretory structures in the pith, but com-parable structures are absent from T. mahoningensis. OtherPennsylvanian and Permian stems, such as the morphotaxaDadoxylon Endlicher, Araucarioxylon Kraus, and Walchio-premnon valdajolense (Mougeot) Florin (Florin 1938–1945)



Fig. 13 Thucydia gen. et sp. nov. SEM photographs of ovulate fertile structures. A, SEM of chemical maceration of the external side of twonodes in an ovulate fertile zone showing bracts (B), positions of dwarf shoots (brackets), fragment of one axillary dwarf shoot (Ds), and sterilescales (sc). Note position and size of each organ. OUPH 13455 (GR16-GY5) #30; mm. B, SEM of maceration of the basal regionscale p 0.5of an axillary fertile shoot. Note the abaxial surface of sporophylls (arrowheads) and sterile scales (sc). OUPH 13455 (GR16-GY26) #44;

mm. C, SEM of the adaxial surface of bract. Note the linear shape, dentate margin (arrow), and broken tip. Also note that the entirescale p 1surface of the bract is covered by papillae. OUPH 13456 (GR15-GX10) #38; mm. D, SEM of the adaxial surface of the bractscale p 0.5showing stomata. Note that stomata are composed of four to six subsidiary cells that bear upright papillae (arrows). Also note that papillaemay be either upright or overarching. OUPH 13456 (GR15-GX12) #500; mm. E, SEM of the abaxial surface of the bract showingscale p 50trichome bases (arrows). Note that trichome bases cover the entire surface, and they are separated by elongated epidermal cells. OUPH 13456(GR15-GX13) #500; mm. F, SEM of sterile scale showing general morphology and cuticular features. Note linear shape and mucronatescale p 50curved apex. Also note that the adaxial surface is covered by papillae (arrowheads), whereas the abaxial surface is relatively smooth (arrow).OUPH 13456 (GR15-GX7) #54; mm. G, SEM of the apical region of the sporophyll. Note that the sporophyll is curved at thescale p 500tip, where a seed scar (arrow) is facing the base of the sporophyll. Also note the lateral folds with small papillae (arrowheads). OUPH 13455(GR16-GY8) #56; mm. H, SEM of the inner surface of the seed coat. Note that the seed has an elliptical shape and a peripheralscale p 500extension (narrow wing) of the seed coat (arrow). OUPH 13456 (GR15-GX1) #100; mm.scale p 200



Table 2

Comparison of Vegetative Morphological Characters for Thucydia mahoningensis and Other Paleozoic Conifers

General group/species/source Stem Lateral branches

Ultimate leaves

Heterophyllya

Penultimate leaves

Length(mm)

Width(mm)

Shape(face view)

Shape(side view)

Angle ofdivergence

Length(mm)

Width(mm)

Shape(face view)

Shape(side view) Base Apex

Walchian Voltziales:Thucydia mahoningensis Orthotropic Plagiotropic 5.0–12.5 1.0–1.5 Nt to Li Sc to Ss 3.0–6.0 0.4–1.0 Nt to Li Sc to Ssb 22–57 21–54 AbsentUtrechtia floriniformis (1) Orthotropic Plagiotropic 12.0–25.0 1.5–3.0 Nt to Li, Fr Sc 9.0–13.0 0.4–0.6 Nt to Li Sc to Ss ? 30 PresentLecrosia grand’euryi (2) ? Irregular 11.0–20.0 1.5 Li Sc 8.0–12.0 1.2 Li? Sc to Sp 40–70 ? Absent?Lebachia parvifolia (2) ? Plagiotropic 4.0–15.0 1.0–2.0 Nt to Li, Fr Sc 2.0–4.5 0.7–1.2 Nt to Li Sc to Ss ? 40 Present?Lebachia garnettensis (2+) ? Plagiotropic 3.0–16.0 1.5–2.5 Nt to Li Sc 4.0–7.0 0.4–1.4 Nt to Li Sc to Ss 35–70 ? AbsentLebachia goeppertiana (2) ? Plagiotropic 2.5–10.0 1.5–2.0 Nt to Li Sc 2.0–8.0 0.5–0.8 Nt to Li Sss ? 35 AbsentOtovicia hypnoides (3) ? Plagiotropic 2.0–8.0 1.0–1.5 St to La Fa to Ssc 1.5–4.0 0.2–0.5 Nt to Li Fac 35–90 35 PresentErnestiodendron filiciforme (2) ? Plagiotropic 10.0–23.0 1.5–3.5 Nt to Li Sc to Spd 7.0–15.0 1.5–2.0 Nt to Li Sp 70–110 15 AbsentEmporia lockardii (4) Orthotropic? Plagiotropic 8–10e 1.0–2.1e Nt to Li Sc to Ss 2.5–5.0e 0.5–1.2e Tr to Li Sc to Ss 10–30e ? Present

Angaran Voltziales:Kungurodendron sharovii (5) ? Plagiotropic to irregular? ?–12.0 ?–3.5 Tr to La Sc 4.0–9.0 1.0–1.25 Tr to La Li to Sc 130 ? AbsentConcholepis harrisii (5) ? Irregular ?–12.0 ?–2.5 Tr? Fa to Sssc ? ? Tr? Fa to Sssc 40–45 ? Absent?Timanostrobus muravievii (5) ? Irregular ? ? La to Sq Sc ? ? La to Sq Sc 130 ? Absent?

Other Late Permian Voltziales:Ullmannia frumentaria (6) ? ? … … Tr to La Fa to Sssc … … Tr to La Fa to Sssc 30–45 ? …Voltzia hexagona (7) ? Irregular 60–150 15–50 Li to Tr Sc 45–60 15–30 Li to Tr Sc 20–45 ? PresentVoltzia liebeana (8) ? Irregular ? ? … … ? ? … … … … ?Majonica alpina (9) ? ? ?–35.0 ?–6.0 Ns to Ov ? 10.0–30.0 3.0–4.0 Ov Sl ? ? May occur?Dolmitia cittertiae (9) ? ? ? ? ? ? 8.0–20.0 4.0–5.0 Ov to Ob ? ? ? ?Ortiseia leonardii (10) ? Plagiotropic 12.0–35.0 ?–8.0 Ob to Ov Sl 6.0–15.0 4.0–7.0 El to Ov Sl 20–45 ? Absent

Sources. 1, Mapes and Rothwell 1991. 2, Florin 1938–1945. 2+, emended by Winston 1984. 3, Kerp et al. 1990; however, leaf measurements were taken from Florin (1938–1945) because such data arenot available in Kerp et al. 1990. 4, Mapes and Rothwell 1984, 1991. 5, Meyen 1997, angles estimated from plates. 6, Goeppert 1850, 1864–1865; Florin 1927, 1938–1945. 7, Schweitzer 1996; however,measurements of leaves were taken directly from the plates. 8, Pseudovoltzia liebeana of Geinitz 1880, Schweitzer 1963, measured from published figures. 9, Clement-Westerhof 1987. 10, Clement-Westerhof1984.

Note. Quantitative characters that have substantially overlapping ranges of variation are considered to be similar, whereas those with disjunct or nearly disjunct ranges are considered to be different.Characters that differ from those of T. mahoningensis are underlined. Leaf shape abbreviations: El p elliptical, Fr p forked tip, Li p linear, Ns p narrow subtriangular, Nt p narrowly triangular, Ob p

oblong, Ov p ovate, Sc p slightly concave, Sl p slightly lanceolate, Sp p spreading, Sq p squamose (pscalelike), Ss p S shaped, Sss p slightly S shaped, St p subtriangular, Tr p triangular.a In this article, “heterophylly” denotes differences in the shape of leaves, where two distinctive types of leaves are known. Other authors (Kerp et al. 1990) may use this term to emphasize differences in

leaf size.b Slightly concave (Sc) and S shaped (Ss) are leaf shapes in the sense of Florin (1938–1945). According to Florin, leaves of Lebachia are (i) slightly concave, where the adaxial side is slightly curved and

concave and the tip is incurved at different angles; (ii) S shaped, where half of the adaxial side is first concave and then bent forward and inward with a pointed tip.c According to Kerp et al. (1990) and Meyen (1997), leaves may be falcate (Fa); however, the definition of “falcate” refers to a slightly convex sickle shape in which the tip of the object (e.g., leaf) is

recurved away from the stem and not incurved toward the stem. Therefore, “falcate” in these articles is equivalent to “slightly concave” in the sense of Florin 1938–1945.d Ernestiodendron filiciforme (Florin 1938–1945) has spreading leaves, where leaves are rotate; they are more or less firm, where the apical portion of the adaxial side is slightly bent and concave or slightly

convex, and the tip is parallel to the main axis of the stem and or slightly concave to it or incurved at an angle of 15�.e Preliminary measurements from original description of bracts (Mapes and Rothwell 1984) and from ongoing research. We have narrowed the possible vegetative shoots to a group with ultimate leaves

that are !0.9 mm long and that probably includes specimens that are 2.5–5.0 mm long.




and several fossil coniferophyte plants, including somecordaiteans (Trivett and Rothwell 1991), Barthelia furcata(Rothwell and Mapes 2001), and Dicranophyllum gallicumGrand’Eury (Renault and Zeiller 1888), have a pith that isseptate rather than parenchymatous as in T. mahoningensis(table 3). The pith of T. mahoningensis and several unnamedconifer shoots from Oklahoma (Rothwell 1982) is character-ized by resin canals, but in the Oklahoma stems, no epitheliallining has been identified.

Thucydia mahoningensis has an endarch eustele and densewood, as do anatomically preserved conifers and confero-phytes in general (Taylor and Taylor 1993). Tracheids of T.mahoningensis have uniseriate bordered pits, as do theOklahoma conifer shoots (Rothwell 1982), S. multinervia (Yaoet al. 2000), and the coniferophyte B. furcata (Rothwell andMapes 2001), whereas other species display unibiseriate (E.lockardii) or unimultiseriate opposite pits (W. valdajolense) orunimultiseriate alternate pits of the Dadoxylon/Araucarioxy-lon type. Rays of T. mahoningensis are parenchymatous anduniseriate, as are rays of other Paleozoic conifers for whichinternal anatomy is known.

Cuticular characters. Cuticular features of the penultimateand ultimate leaves are similar in T. mahoningensis (table 1).The adaxial surface has two bands of monocyclic stomata thatare separated by a stomatal free zone, and the abaxial surfaceis covered by evenly distributed trichome bases and inter-spersed ordinary epidermal cells. This “hyperstomatic” cutic-ular pattern has not been found previously in Paleozoic con-ifers, but the Upper Pennsylvanian conifer-like coniferophyteB. furcata has a similar stomatal distribution pattern on veg-etative leaves (Rothwell and Mapes 2001).

All other walchian conifers for which cuticles are knowndisplay amphistomatic leaves (Florin 1938–1945; Clement-Westerhof 1984; Mapes and Rothwell 1991; table 3). In E.filiciforme (Florin 1938–1945), species of Ortiseia (Clement-Westerhof 1984), and an unnamed walchian species fromHamilton, Kansas (Liu et al. 2000; Rothwell and Mapes 2001),stomata are distributed primarily in uniseriate, longitudinallyoriented rows. By contrast, there are two adaxial bands ofstomata and a smaller number of stomata, either in short bandsor irregularly placed on the abaxial surface of leaves, in U.floriniformis (Mapes and Rothwell 1991), species assigned toLebachia by Florin (1938–1945), Otovicia hypnoides (Kerpet al. 1990), E. lockardii (Mapes and Rothwell 1991; table 3),and two unnamed species from Hamilton, Kansas (Liu et al.2000). Some nonconifer Paleozoic coniferophytes, includingspecies of Dicranophyllum, are hypostomatic, with stomatadistributed in two abaxial grooves (Barthel 1977; Rothwelland Mapes 2001). That pattern has not been found in Paleo-zoic conifers.

Thucydia mahoningensis is the only species of Paleozoic con-ifers for which stomatal distributions of the vegetative leavesare known to be dissimilar from those of fertile leaves. Whereasthere are two adaxial stomatal bands on vegetative Thucydialeaves, the ovuliferous bracts, pollen cone bracts, and sterilescales of both ovuliferous and polliniferous dwarf shoots allhave stomata evenly distributed over their entire adaxial epi-dermis (table 1). All other walchian species either have beencharacterized by stomatal distribution patterns that are similaron both vegetative leaves and fertile leaves or have been as-

sumed to display such similarity. This was a basic assumptionthat Florin introduced as a presumably reliable means of rec-ognizing European and other walchian taxa. The stomatal dis-tribution patterns of both vegetative leaves and ovulate conebracts in E. lockardii (Mapes and Rothwell 1984, 1991) aresimilar to one another. In that sense, they are like E. filiciforme(Florin 1938–1945), species of Ortiseia (Clement-Westerhof1984), and several species described as Lebachia by Florin(1938–1945). The discovery that T. mahoningensis has differ-ing patterns of stomatal distribution on vegetative and fertileleaves (table 1), however, demonstrates that such charactersare not always consistent within a walchian species. The wide-spread perception that stomatal patterns are uniform acrossall walchian organs, and therefore diagnostic of walchian con-ifer species, is in need of careful reevaluation and species-by-species confirmation.

Pollen cones. Thucydia mahoningensis provides the firstunequivocal evidence for compound pollen cones in Paleozoicconifers and is the only conifer known to display structuralequivalence of ovule- and pollen-producing fructifications.Both are compound shoot systems that consist of a main axisthat bears bracts and axillary fertile dwarf shoots (fig. 14). Inboth fertile systems, the axillary shoots produce several sterilescales, and sporophylls occur only on the side of the dwarfshoot that faces the main axis of the fructification. Other thandissimilarities in the sizes and numbers of parts, the two differprimarily by the ovuliferous fructification being a fertile zone,with an inverted ovule on each sporophyll of the dwarf shoots,whereas the pollen cones are terminal on the branches, withan erect pollen sac on each sporophyll of the dwarf shoots.

As emphasized above, all previously reported conifer pollencones from the Late Pennsylvanian (or Upper Carboniferous)and Early Permian either are simple shoots (Florin 1950, 1951;Clement-Westerhof 1984; Mapes and Rothwell 1998) or havean organization that is equivalent to a simple shoot (e.g., pl.6, fig. 1, of Kerp et al. 1990). Most Mesozoic and Cenozoicfossil conifers and modern conifers clearly have simple pollencones, but a few have been interpreted as compound by someauthors (Kerp et al. 1990; Grauvogel-Stamm and Galtier 1998;Mapes and Rothwell 1998). A summary and discussion ofthose pollen cones is presented elsewhere (Rothwell and Mapes2001).

Ovulate fertile zones. Organization of the ovulate fertilezones in T. mahoningensis is equivalent to that of compoundterminal cones of Paleozoic conifers and most coniferophytes(Rothwell and Mapes 2001). The ovulate fructifications of T.mahoningensis are compound shoot systems, with ovuliferousdwarf shoots attached to the axis in the axils of helically ar-ranged bracts. The ovuliferous dwarf shoots of Thucydia arebilateral, with sterile scales basally and an inverted ovule at-tached to the tip of each sporophyll (figs. 12, 14). In all thesefeatures, Thucydia conforms to the general morphology ofpreviously described walchian ovulate cones (Kerp andClement-Westerhof 1991). The greatest difference between theovulate fructifications of Thucydia and those of other knownwalchian species from Euramerica is that Thucydia does notform terminal cones. Instead, the primary axis of ovulate Thu-cydia fertile zones continues to grow and produces a vegetativeregion distally. In this respect, Thucydia is similar to the Per-mian conifers C. harrisii Meyen and V. hexagona (Bischoff)



Table 3

Comparison of Cuticular Features for Ultimate Leaves of Thucydia mahoningensis and Other Paleozoic Conifers

General group/species/source

Stomataldistribution

adaxial

Stomataldistribution

abaxial

Stomatalcomplexstructure

Stomatalcomplex size

(mm)

Subsidiarycell

number

Subsidiarycell

papillaeMarginaltrichomes

Trichomebasesadaxial

Trichomebasesabaxial

Epidermalpapillaeadaxial

Epidermalpapillaeabaxial

Walchian Voltziales:Thucydia mahoningensis Two long bands Absent Monocyclic 24 # 20 6–8 Present Long/short,

hairlikeAbsent Present, abundant Present Absent

Utrechtia floriniformis (1) Two long bands Two shortbands,variable

Monocyclic 50 # 55 5–9 Present Short, hairlike Present Present, abundant Present Present

Lebachia parvifolia (2) Two long bands Two shortbands

Monocyclic 50 # 40a 6–8 Present Short, hairlike Present Present, abundant Present ?

Lebachia garnettensis (2) Two long bands Few, scattered Monocyclic 45 # 40a Many (110?) Absent Short, hairlike Absent Present, abundant ? ?Lebachia goeppertiana (2) Two long bands Two short

bandsMonocyclic,

incompletelydicyclic

55 # 42a 4–6 More or less Absent Present Present, abundant Absent? Absent?

Lecrosia grand’euryi (2) ? ? ? ? ? ? ? ? ? ? ?Otovicia hypnoides (3) Two long bands Few stomata

groupsMonocyclic,

incompletelydicyclic

70 # 60 5–8 Present Conical Present Present, abundant Present Present

Ernestiodendron filiciforme (2) Parallel rows Parallel rows Monocyclic,incompletelydicyclic

60 # 40a 4–8 Present Short, hairlike Present Present, abundant Absent Present

Emporia lockardii (4) Two long bands Two bands Monocyclic 58–46b 5–9b Present Long/short ? ? Present PresentAngaran Voltziales:

Kungurodendron sharovii (5) Two bands Few stomatagroups

Monocyclic ? 5–8 More or less Short,papilla-like

Present Absent Present Absent

Concholepis harrisii (5) ? ? ? ? ? ? Present? ? ? ? ?Timanostrobus muravievii (5) Indistinct short

rows,scattered

Indistinctshort rows,scattered

Monocyclic ? 5–6 Absent? Short? ? ?? ?

Other Late Permian Voltziales:Voltzia hexagona (6) ? ? ? ? ? ? ? ? ? ? ?Majonica alpina (7) Interrupted rows Interrupted

rows to norows

? 75 5–10 Present Absent ? ? Present? Present?

Dolmitia cittertiae (7) Interrupted rowsor scattered

Scattered Monocyclic 90 5–10 Present Short and wide ? ? ? Sometimes

Ortiseia leonardii (8) Parallel rows Parallel rows Dicyclic 65 4–7 Present Absent? Present,abundant

Present, abundant Present Present

Sources. 1, Mapes and Rothwell 1991. 2, Florin 1938–1945. 3, Kerp et al. 1990. 4, Mapes and Rothwell 1991. 5, Meyen 1997. 6, Schweitzer 1996. 7, Clement-Westerhof 1987. 8, Clement-Westerhof1984.

Note. Characters that differ from those of T. mahoningensis are underlined.a Measured directly from Florin’s monograph (1938–1945).b Measured from photographs of Mapes and Rothwell (1984).




Geinitz (table 4) and to several Paleozoic coniferophytes, in-cluding Trichopitys heteromorpha Saporta, Dicranophyllumhallei Remy and Remy, D. gallicum Grand’Eury, and B. furcataRothwell and Mapes (table 3 of Rothwell and Mapes 2001).A small number of ovulate fertile zones were described byFlorin (1938–1945) and were interpreted to be anomaliesamong walchian conifers, as they are in living conifers (Cham-berlain 1935; Florin 1950). However, the more recent recog-nition that this morphology is a consistent feature of severalspecies of fossil conifers and other coniferophytes indicates thatFlorin’s “anomalous” specimens (Florin 1938–1945, 1950)may actually characterize additional walchian species. Reso-lution of this question awaits discovery and more thoroughcharacterization of larger numbers of ovulate walchian spec-imens from Upper Carboniferous and Lower Permian depositsof Europe and North America.

Ovuliferous dwarf shoots. Ovuliferous dwarf shoot mor-phology differs among the various groups of Paleozoic coni-fers. Species of the South American Ferugliocladaceae havesimple ovuliferous dwarf shoots, consisting only of an erectterminal ovule in the axil of each bract (Archangelsky andCuneo 1987; Rothwell and Mapes 2001). The Angaran speciesK. sharovii, C. harrisii, and T. muravievii have dwarf shootsthat are nearly radial, with large numbers of vegetative scalesand several interspersed ovulate sporophylls, and in this re-spect, these species are more like nonconifer Paleozoic coni-ferophytes than other conifers (table 2 of Rothwell and Mapes2001). Ovuliferous dwarf shoots of those Angara conifers arescored as nonradial in table 4, primarily because the sporo-phylls are all located on the same side of the dwarf shoot (i.e.,facing the cone axis).

Ovuliferous dwarf shoots of the other Paleozoic conifers aredistinctly bilateral. All are more or less flattened, have fewersterile scales than the Angara species, and tend to have fewersporophylls on the side of the dwarf shoot that bears the ovules(i.e., facing the main axis) than are found in the Angara species(table 4). In some walchian species, there are two or moresporophylls interspersed among the vegetative scales below theapex of the dwarf shoots (i.e., E. lockardii, O. hypnoides, andsome specimens of Walchiostrobus Florin), whereas in otherspecies, including T. mahoningensis, the dwarf shoot termi-nates in sporophylls or in ovule-bearing structures of uncertainhomologies (i.e., “fertile scales” sensu Mapes and Rothwell1991; table 4).

In V. hexagona, V. liebeana sensu Schweitzer (1996), M.alpina, and O. leonardii, the ovuliferous dwarf shoots are evenmore flattened than in the walchian species; most have fewerand more or less interconnected sterile scales and sporophylls/fertile scales at the apex (table 2). These species also lack sterilescales on the side of the dwarf shoot that faces the main axis.In U. frumentaria, the ovuliferous dwarf shoot appears to con-sist of a simple structure (table 2). In that feature, it mayrepresent either a very broad sporophyll or an evolutionarilysimplified ovuliferous dwarf shoot (i.e., ovuliferous scale ofmodern conifers sensu Florin 1951).

Taxonomic Concepts for Walchian Conifers

The vast majority of walchian conifer species are representedonly by vegetative branches and are characterized by features

such as leaf morphology and size, angles of leaf divergence,and, when present, branching pattern (Florin 1938–1945;Clement-Westerhof 1984; Visscher et al. 1986). Clement-Westerhof (1984) lists 65 species that fall within that category,and there are at least 22 more walchian species based on spec-imens that also display cuticular characters (Florin1938–1945; Clement-Westerhof 1984; Kerp et al. 1990; Ma-pes and Rothwell 1991). Descriptions of walchian species varytremendously in accuracy and completeness, and reliable com-parative criteria for distinguishing among species have notbeen developed. Some of the most complete and accurate de-scriptions are presented by Florin (1938–1945), but evenFlorin’s diagnoses and descriptions of most species (Florin1938–1945) do not include detailed suites of contrasting char-acters that can be used to separate species or to identifyspecimens.

Florin does illustrate rather precise concepts for several spe-cies in the form of drawings of ultimate leafy shoots (Textabb.14–16 of Florin 1938–1945; fig. 26 of Florin 1951). Thesedrawings clearly reflect Florin’s idealized concepts of the var-ious species, but many of the drawings are quite similar to oneanother, and none considers possible ranges of variation withina single species. Examination of the specimens figured by Florinas each of those species (i.e., Taf. 1–152, 155–156, and161–164 of Florin 1938–1945) reveals considerable variationin branching angles, leaf shapes, leaf sizes, and angles of leafdivergence, variations that are not reflected by Florin’s ideal-ized drawings or in the diagnoses of the various species. Inreality, the range of morphological variation displayed by in-dividual specimens and by groups of specimens assigned tomost of Florin’s species (Florin 1938–1945) is greater than thedifferences between the species (e.g., table 2).

Florin provides a dichotomous key (i.e., pp. 329–336 ofFlorin 1938–1945) to help in the identification of specimens.However, the characters used in Florin’s key also do not ac-count for ranges of variation within any of the species. Rather,they appear to reflect his idealized concepts of characters foreach species. Therefore, to date no morphological charactersof vegetative organs have been identified that can be used toadequately characterize most walchian species, to separate sim-ilar species from each other, or to identify new specimens toany but the most distinctive walchian species.

Florin recognized the taxonomic inadequacy of morpholog-ical characters alone and developed a suite of useful cuticularcharacters in the early stages of his walchian conifer studies(Florin 1927). Florin was able to show convincingly that theleaves of E. filiciforme have quite different stomatal distri-butions than species he assigned to the genus Lebachia, andhe used these characters in the diagnoses of the various species(Florin 1938–1945). Unfortunately, cuticular characters ap-pear to be less distinctive for the various species of Lebachiathan generally believed. The specific diagnoses presented byFlorin (1938–1945) include a few general cuticular characters,but with the exception of E. filiciforme, these cuticular char-acters are not diagnostic for any of the species (Florin1938–1945).

The cuticular characters used by Florin in his diagnoses anddescriptions of specimens (Florin 1938–1945) are presented intable 3. These are supplemented by several additional char-acters used by Clement-Westerhof (1984) to distinguish among




species of Ortiseia (table 3). The supplemental cuticular char-acters included in table 3 are limited to those that can bedetermined or measured from the figures of Florin(1938–1945), and the sampling is less complete than presentedfor Ortiseia by Clement-Westerhof (1984). Nevertheless, thesecharacters demonstrate that most of Florin’s species cannot berecognized by the cuticular characters he developed (table 3).From this analysis, it is clear that the taxonomic utility ofcuticular characters for differentiating among species of wal-chian conifers is more limited than was popularly believed.

Fertile Organs in Walchian Conifer Taxonomy

Fertile organs have proven to be extremely valuable in tax-onomic and systematic studies of most vascular plants and areused extensively for defining genera and families of walchianconifers (Florin 1938–1945; Clement-Westerhof 1984; Kerp etal. 1990; Kerp and Clement-Westerhof 1991; Mapes and Roth-well 1991). Unfortunately, fertile organs are not known formost walchian conifer species. Even species for which fertileorgans have been described are almost all typified by vegetativebranches. These include E. filiciforme (Schlotheim) Florin, L.frondosa (Renault) Florin, L. garnettensis Florin, L. goepper-tiana Florin, Lebachia parvifolia Florin, L. grand’euryi Florin,Ortiseia jonkeri Clement-Westerhof, O. leonardii Florin, O.visscheri Clement-Westerhof, O. hypnoides (Brongniart) Kerpet al. (pL. hypnoides [Brongniart] Florin), W. (E.?) arnhardtiiFlorin, W. (E.?) germanica Florin, and Walchia (Lebachia?)schlotheimii Brongniart ex Renault (Brongniart 1828–1836;Renault 1885; Florin 1938–1945; Clement-Westerhof 1984).

All of the type specimens for these species occur in mixedconifer assemblages (Florin 1938–1945; Clement-Westerhof1984). Therefore, the correct assignment of cones to each spe-cies relies on the fertile organs having diagnostic morpholog-ical and cuticular characters that convincingly relate them tothe vegetative type specimen. However, as detailed above, mostspecies of walchian conifers are not known to have vegetativecharacters that allow them to be distinguished from severalother walchian species. Therefore, almost all assignments offertile organs to species of vegetative remains in mixed coniferassemblages must be viewed as tentative. Among walchianconifers, only T. mahoningensis, E. lockardii (Mapes andRothwell 1984), and U. floriniformis (Mapes and Rothwell1991) are typified by specimens that display ovulate fructifi-cations, so there is no question about which ovulate organsbelong to these species.

Clement-Westerhof (1984) presents a detailed suite of mor-phological and cuticular characters to distinguish among andhelp identify specimens of Ortiseia junkeri, O. leonardii, andO. visscheri from mixed assemblages. Other authors are lessspecific about their taxonomic assignments of fertile walchianconifer organs. Florin’s justification for assigning ovulate conesto L. piniformis is typical. The two most well prepared andinformative cones assigned to L. piniformis are figured on (a)Taf. 15–16, Abb. 1–14 and (b) Taf. 17–18, Abb. 11–24; Taf.19–20, Abb. 1–30; Taf. 21–22, Abb. 1–12 of Florin(1938–1945) and are related to vegetative remains of L. pin-iformis by the statements (a) “Hausdorf bei Neurode—Außereinzelnen Fragmenten von Seitenzweigen letzter Ordnung, diezu Lebachia piniformis gehoren konnen, liegt hier der in Abb.

1, Taf. XV/XVI, dargestellte, junge weibliche Zapfen als Ab-druck mit anhaftenden, zusammengedruckten Resten der or-ganischen Substanz vor” (pp. 41–42 of Florin 1938–1945) and“Die Bestimmung grundet sich darauf, daß der Zapfen in sei-nem Bau vollig mit dem zur genannten Art gehorenden undin Abb. 1, Taf. XIX, dargestellten Zapfen von Ottendorf beiBranau ubereinstimmt. Ich weise hier generell auf die unten-stehende, eingehende Beschreibung des Ottendorfer Zapfenshin und werde mich uber den Olberg-Zapfen kurzer fassen”(p. 42 of Florin 1938–1945) and (b) “Aus dieser Beschreibungsowie aus einem Vergleich mit dem Typematerial geht un-zweideutig hervor, daß es sich in Bezug auf das OttendorferMaterial um Lebachia piniformis handelt und daß also der inAbb. 1, Taf. XIX/XX, abgebildete weibliche Zapfen zu dieserArt gehort” (p. 44 of Florin 1938–1945), respectively. In short,Florin’s justifications reflect his general impressions or “Ge-stalt” of relationships, since no specific characters areidentified.

For the remaining walchian species, there is similar or evengreater doubt regarding cone identifications. For example, allof the cones and isolated ovuliferous dwarf shoots figured byFlorin (1938–1945) as specimens of W. (E.?) germanica Florinhave been segregated by Kerp and Clement-Westerhof (1991)as species of Thuringiostrobus. However, no specific charactersof individual specimens are documented by either Florin(1938–1945) or Kerp and Clement-Westerhof (1991; see alsoClement-Westerhof 1988) to support either the assignment orthe removal of the specimens from W. (E.?) germanica. There-fore, there are no data to help other workers decide which (ifeither) of these taxonomic opinions is correct. We do not knowto what extent other assignments of fertile organs to speciesof walchian conifers by Florin and others are incorrect. How-ever, in the absence of specific criteria for confirming or re-jecting such assignments, each must be viewed with cautionuntil objective criteria are developed that allow workers tobase taxonomic decisions on specific characters. The specific,detailed characters that have been developed for identifyingspecimens of T. mahoningensis and species of Ortiseia(Clement-Westerhof 1984) are important steps in thatdirection.

We do not wish to discount the importance of ovulate“cone” characters in systematic studies of walchian conifers.Indeed, within the much larger set of informative charactersthat is available to walchian conifer systematics (tables 2–4),we consider them to play an important role. For example, theovulate fructification of T. mahoningensis contributes severalcharacters to the generic and familial circumscriptions (table4).

Comparison of Ovulate Fructifications in Thucydiaand Other Paleozoic Conifers

As stressed above, T. mahoningensis has ovulate fertilezones, whereas other walchian conifers have terminal ovulatecones. Additional informative characters of Thucydia ovulatefructifications include shape of the bract, relationship of thebract to the dwarf shoot, symmetry of the dwarf shoot, num-bers and positions of sterile scales, morphology of sterile scales,position and morphology of sporophylls, number of sporo-phylls, and mode of attachment of the ovules.




Fig. 14 Diagrams showing organization of fertile dwarf shoots aspictured in cross sections and oriented by position of the subtendingbract (B). Location of the cone axis is above each diagram. A, Ovu-liferous dwarf shoot with four numbered sporophylls at apex andsterile scales arranged around base of shoot axis. B, Polliniferousdwarfshoot with four numbered sporophylls (terminal pollen sacs) posi-tioned toward cone axis (white circle) and sterile scales on other threesides of axis.

Thucydia mahoningensis has three to four narrow sporo-phylls terminating the flattened dwarf shoot and 10–15 sterilescales basally (figs. 12, 14A). In these features, Thucydia ismost similar to Walchiostrobus (Lebachia?) gothanii Florinand some specimens described as Walchiostrobus sp. by Florin(1938–1945). The number of sterile scales in T. mahoningensisis also similar to E. filiciforme, as interpreted by Clement-Westerhof (1984). However, the number of sporophylls in E.filiciforme is less clear. Florin (1938–1945) describes three toseven megasporophylls for this species, but Clement-Westerhof(1984) recognizes only one (Kerp et al. 1990). The relativemerits of these interpretations are hard to interpret. This isbecause numbers of sporophylls produced by an individualshort shoot are not clearly shown by side views of many wal-chian ovuliferous dwarf shoots (e.g., figs. 11B, 12A), such asmost of the figures of E. filiciforme illustrated by Florin(1938–1945). We do not consider any of the interpretationsfor the structure of the ovuliferous dwarf shoots assigned toE. filiciforme (Florin 1938–1945; Clement-Westerhof 1984;Kerp and Clement-Westerhof 1991) or Walchianthus (Florin

1938–1945; Kerp and Clement-Westerhof 1991) to be sup-ported by convincing data. If Florin’s interpretation of Ernes-tiodendron is correct, then Thucydia and Ernestiodendronhave overlapping ranges of variation in sporophyll numbers.Ranges in variation for numbers of sporophylls and sterilescales also overlap with specimens of L. parvifolia Florin andwith some specimens of Walchiostrobus described by Florin(1938–1945). Larger numbers of ovuliferous dwarf shoot spec-imens will have to be characterized for several species of wal-chian conifers before adequate data are available to determinethe taxonomic and systematic significance of sporophyll andsterile scale numbers among walchian conifers.

Ovuliferous dwarf shoots of T. mahoningensis are also sim-ilar to those of U. floriniformis in several respects (table 4).This latter species differs from T. mahoningensis in numbersof sporophylls (or fertile scales) and sterile scales (Florin1938–1945; Kerp and Clement-Westerhof 1991), but bothhave obvious terminal sporophylls (or one fertile scale) andsterile scales basally. Emporia lockardii, O. hypnoides, and allthree species of Otovicia are less similar to T. mahoningensisbecause they have the sporophylls interspersed among the ster-ile scales (Clement-Westerhof 1984; Mapes and Rothwell1984, 1991; Kerp and Clement-Westerhof 1991; table 4). Asdiscussed above, the ovuliferous dwarf shoots of the Angaranconifers, the South American Ferugliocladaceae, and the LatePermian voltzialean conifers all differ even more from T. ma-honingensis (table 4).

Walchian Nomenclature

Unfortunately, some of the most famous and commonly usednames for walchian conifers either are nomenclaturally ille-gitimate or taxonomically incorrect. To address these prob-lems, one group of workers (Visscher et al. 1986) has proposeda series of taxonomic and nomenclatural revisions for walchianconifers (and other fossils) that follow a novel system for pro-moting names and concepts of fossil taxa as new informationaccumulates (Clement-Westerhof 1984, 1987, 1988; Visscheret al. 1986; Kerp et al. 1990; Kerp and Clement-Westerhof1991). These articles add new data for species of Ortiseia andO. hypnoides, offer new interpretations of previously de-scribed specimens of several genera and species, revise severaltaxonomic concepts of many of Florin’s genera and species,choose type species for genera, typify species, describe newgenera and species, and propose new names for previouslydescribed taxa (Clement-Westerhof 1984; Visscher et al. 1986;Kerp et al. 1990; Kerp and Clement-Westerhof 1991). Al-though these studies help clarify some aspects of walchiantaxonomy and nomenclature, some of the reinterpretations arenot supported by new data or references to specific charactersof previously described specimens. Other proposals by theseauthors were in conflict with the rules of nomenclature whenproposed and if adopted would lead to nomenclatural insta-bility (Mapes and Rothwell 1991).

Clement-Westerhof (1984) emphasizes that Lebachia Florinis typified by the same specimen as the preexisting genus Wal-chia (Sternberg) and, therefore, that Lebachia is an illegitimatename. Kerp et al. (1990) point out that the name E. filiciforme(Schlotheim) Florin was incorrectly chosen from among com-peting epithets for the species. We agree with the reasoning of



Table 4

Comparison of Ovulate Fertile Zone Characters for Thucydia mahoningensis and Comparable Ovulate Organs of Other Paleozoic Conifers

General group/species/source Ovulate fructification

Cone morphology

Bract

Dwarfshoot

symmetry

Number ofsterilescales

Position ofsporophyll(s)

Number ofsporophylls/fertile scales Ovules

Length(cm)

Width(cm) Shape

Walchian Voltziales:Thucydia mahoningensis Fertile zone 3.0–4.5 0.9–1.5 Cylindrical to ellipsoidal Simple Bilateral 10–15 Terminal 3–4 Terminal, invertedUtrechtia floriniformis (1) Terminal cone Up to 7.0 1.2 Cylindrical to ellipsoidal Forked Bilateral 110 Terminal 1 Terminal, invertedLebachia parvifolia (2) Terminal cone? 3.0 2.0 Cylindrical to ellipsoidal Forked Bilateral? 5–10? ? ≥2?a ?Lebachia garnettensis (2) Terminal cone 2.0–3.0 0.10–0.15 Ellipsoidal Forked Bilateral !5? ? ≥3?a ?Lebachia goeppertiana (2) Terminal cone 3.0 1.5 Cylindrical Simple Bilateral 110 ? ? ?Lecrosia grand’euryi (2) Terminal budlike structure? 2.0 1.3 Ovate Simple ? ? ? ? ?Otovicia hypnoides (3) Terminal cone 3.0–6.5 1.1–1.8 Cylindrical Forked Bilateral 110 Interspersed

with SS2 Terminal, inverted

Ernestiodendron filiciforme (2) Terminal cone 10.0–20.0 2.2–3.0 Ellipsoidal Forked Bilateral 5–10 Terminal? 1 Terminal, invertedWalchiostrobus gothanii (4) Terminal cone 12.0b 2.0–2.5b Ellipsoidal Forked Bilateral !5 Terminal? 1 Terminal, invertedEmporia lockardii (5) Terminal cone 5.0 1.5 Cylindrical to ellipsoidal Forked Bilateral 14–30 Interspersed

with SS1–3 Terminal, inverted

Cathaysian Voltziales:Batenburgia sakmarica (6) Terminal cone 2.4 3.1 Cylindrical to ellipsoidal Two lateral extensions ? 8–12 ? 1 or 2? ?

Angaran Voltziales:Kungurodendron sharovii (7) ? Up to 7.0 3.0 Cylindrical to ellipsoidal Simple Nonradialc 110 Interspersed

with SSCa. 10 Terminal, inverted

Concholepis harrisii (7) Fertile zone Up to 12.0 ? Cylindrical? Simple Nonradialc 110 Interspersedwith SS

Ca. 2 Terminal, inverted?

Timanostrobus muravievii (7) Terminal cone? Up to 11.0 4.0 Cylindrical ? Bilateral 110 Interspersedwith SS

110 Terminal, inverted

Other Late Permian Voltziales:Ullmannia frumentaria (8) Terminal cone? ? ? ? Simple Bilateral None Terminal 1 Surficial, invertedVoltzia hexagona (9) Fertile zone 8.5–10.0 3.5–5.0 Cylindrical to ellipsoidal Simple Bilateral !5 Terminal 3 Surficial, invertedVoltzia liebeana (10) Terminal cone ? 4? ? Simple Bilateral 2 Terminal 3 Surficial, invertedMajonica alpina (11) ? ? ? ? Simple Bilateral 1–5 Terminal? 2 Surficial, invertedDolmitia cittertiae (11) ? ? ? ? Simple Bilateral 110 Terminal? 3 Surficial, invertedOrtiseia leonardii (12) Terminal cone? 6.0 2.0 Cylindrical to ellipsoidal Simple Bilateral 110 Interspersed

with SS1 Surficial? inverted

Sources. 1, Mapes and Rothwell 1991. 2, Florin 1938–1945. 3, Kerp et al. 1990. 4, Kerp and Clement-Westerhof 1991. 5, Mapes and Rothwell 1991. 6, Hilton and Geng 1998. 7, Meyen 1997. 8, Goeppert1850, 1864–1865; Florin 1927, 1938–1945. 9, Schweitzer 1996. 10, as Pseudovoltzia liebeana in Schweitzer 1963. 11, Clement-Westerhof 1987. 12, Clement-Westerhof 1984.

Note. Characters that differ from those of T. mahoningensis are underlined.a Fertile scale as in Florin, Clement-Westerhof, and Kerp concepts.b Measurements from incomplete cones in Florin (1938–1945).c Where dwarf shoot symmetry is radial, sterile scales and sporophylls are helically arranged, but sporophyll distal region always faces the adaxial side of the shoot.




Kerp et al. (1990) that the correct name for specimens widelyknown as E. filiciforme is actually E. affinis. However, thatcombination has not been formally proposed.

The situation with Lebachia is more complicated. Clement-Westerhof (1984) follows a rationale explained by Visscher etal. (1986) to allow the same names to be used for changingconcepts of fossil taxa as information about each increases,and he proposes that the genus Walchia Sternberg be promotedfrom the status of a form genus (sensu Florin 1927) to a genusof plants. Clement-Westerhof (1984) also proposes that thefamily Walchiaceae be formally recognized for the concept ofLebachiaceae Florin.

The type species of Walchia, Walchia piniformis Sternberg,is typified by a leafy branch that lacks fertile organs, cuticularcharacters, or anatomical characters, and that specimen hasmorphological characters that are common to several speciesof plants assigned to Lebachia sensu Florin (Mapes and Roth-well 1991; table 2). The type specimen of W. piniformis isderived from the same beds (i.e., Toldlauterer Schichten ofThuringer Wald) that also yield several other walchian species(i.e., Lebachia angustifolia, L. frondosa, L. goeppertiana, L.laxifolia, L. parvifolia, and O. hypnoides; table 1 of Florin1938–1945). Therefore, we shall never know which (if any)of the walchian plants with vegetative characters that overlapwith those of W. piniformis are conspecific with the type spec-imen of W. piniformis.

Because the holotype of W. piniformis is not diagnostic ofa particular species of walchian plant, Mapes and Rothwell(1991) retained Walchia sensu Florin (1938–1945) as a formgenus for vegetative remains that are common to several generaand species of walchian conifers (Mapes and Rothwell 1991).These authors proposed the new name U. floriniformis Mapesand Rothwell (1991) for walchian plants that conform toFlorin’s concept of L. piniformis, and they designated U. flor-iniformis as the generitype for the family Utrechtiaceae Mapesand Rothwell (1991). Utrechtia floriniformis is typified by aspecimen that includes an ovulate cone and displays cuticularas well as morphological characters (i.e., Taf. 17–18, Abb.11–24; Taf. 19–20, Abb. 1–30; Taf. 21–22, Abb. 10012 ofFlorin 1938–1945). Therefore, there is no question as to theidentity of this species of fossil plants, even though it has veg-etative morphological characters at the base of the cone thatoverlap with those of numerous other walchian conifers.

A full analysis and discussion of the outstanding questionsabout taxonomy and nomenclature of walchian conifers is be-yond the scope of this investigation. For now, the most con-servative approach is to use established names and concepts,unless compelling evidence is presented with new proposals.For the purposes of this article, we accept and adhere to theconcepts of Culmitzschia sensu Ullrich (1964), Ortiseia sensuClement-Westerhof (1984), Otovicia sensu Kerp et al. (1990),Utrechtia sensu Mapes and Rothwell (1991), Walchia sensuFlorin (1927, 1938–1945), Walchianthus sensu Florin(1938–1945), and Walchiostrobus sensu Florin (1938–1945).As explained by Mapes and Rothwell (1991), HermitiaVisscher et al. and Thuringiostrobus Kerp and Clement-Westerhof are superfluous names (i.e., synonyms of WalchiaSternberg and Walchiostrobus Florin, respectively).

At the 1999 International Botanical Congress, held in St.Louis, fossil plant nomenclature was substantially revised. The

concept of the form genus was abandoned. Under the newrules of botanical nomenclature (Greuter et al. 2000), namesfor plant fossils represent either morphotaxa or biological taxaof extinct plants. Taxa of fossils may be considered as mor-photaxa unless they are understood as plants. Thucydia ma-honingensis, Utrechtia floriniforms, and E. lockardii are cur-rently the three best known species of fossil walchian coniferplants, and each is the generitype for a family of the Voltziales.

By contrast, the type species of Walchia Sternberg, W. pin-iformis, is typified by the part of the sporophyte of a walchianconifer that shows only morphological features of a vegetative,plagiotropic branch. Therefore, Walchia Sternberg is a mor-photaxon, as defined by Article 1.2 of the St. Louis code (i.e.,“A morphotaxon is defined as a fossil taxon which, for no-menclatural purposes, comprises only the parts, life-historystages, or preservational states represented by the correspond-ing nomenclatural type”; Greuter et al. 2000). Mapes andRothwell (1991) originally rejected the Walchiaceae sensuClement-Westerhof (1984) because form genera were definedby their exclusion from a family of plants. Other names forPaleozoic coniferous vegetative branches that conform to thedefinition of a morphotaxon include Buriadia Seward andSahni (sensu Chandra et al. 1999), Carpenteria Nemejc andAugusta, Culmitzchia Ulrich, Curionia Sordelli, Feysia Broutinand Kerp, Gomphostrobus Marion, Paleotaxites White, Par-anocladus Florin, Quadrocladus Madler, Walkomia Florin,and several genera discussed by Meyen (1997) from Permianstrata of Angara. Unless the apical budlike structure figuredby Florin (Taf. 161–162, Abb. 16 of Florin 1938–1945; table4) is an ovulate fructification with diagnostic characters, Lec-rosia Florin also comprises a morphotaxon of vegetativeremains.

Clement-Westerhof (1984) has transferred several other spe-cies of Lebachia plants to Walchia. However, since the mor-phogenus Walchia is inappropriate for species of plants, thesespecies now need to be transferred to another genus (or gen-era). We recommend that such transfers be deferred until thecones assigned to each species are (1) more fully characterizedand (2) confirmed as belonging to the same species as thevegetative type specimen for each. In the interim, we are con-tinuing to use the illegitimate genus name Lebachia for thosespecies (tables 2–4).

Systematic Relationships among Walchian Conifers

In contrast to the species concepts discussed above (that arebased almost entirely on vegetative characters), classificationsof walchian conifers traditionally have relied heavily on ovu-late cone morphology, in which axillary dwarf shoots providemost of the defining characters for genera and families (Florin1938-1945, 1950, 1951; Visscher et al. 1986; Clement-Westerhof 1988; Kerp and Clement-Westerhof 1991; Mapesand Rothwell 1991; Meyen 1997). Circumscriptions of thegenus Thucydia and the family Thucydiaceae depart from thattradition by employing characters that are drawn from all or-gans of the sporophyte and by emphasizing novel charactercombinations that do not occur in other genera and familiesof conifer plants (tables 1–4). Although this approach is rel-atively unique for fossil conifer studies, it is not new. Ourgeneric and familial circumscriptions merely implement the




“whole-plant” approach initiated by Florin in his earliest sys-tematic treatment of walchian conifers (Florin 1927).

If T. mahoningensis were classified primarily by charactersof the ovulate fructifications (particularly ovuliferous dwarfshoots), then we would consider this species to be most closelyrelated to some species that are placed in the Walchiaceae sensuKerp et al. (1990; i.e., W. gothanii and E. filiciforme) and lessclosely related to other species (i.e., E. lockardii, O. hypnoides,Ortiseia junkeri, O. leonardii, and O. visscherii) placed in thesame family by some authors (Kerp and Clement-Westerhof1991) and in two different families (i.e., Emporiaceae andUtrechtiaceae) by other authors (Mapes and Rothwell 1991).However, characters of all the other plant organs reveal thatT. mahoningensis is probably less closely related to all of theseother walchian species than they are to each other. Much morecomplete characterizations of most walchian species (i.e., thosethat emphasize all of the organs of the sporophyte) are requiredfor improving our understanding of systematic relationshipsamong the Thucydiaceae and other families of primitive Pa-leozoic conifers.

Summary and Prospects for Continuing Studies

Thucydiaceae is the most distinctive and completely char-acterized family of primitive Paleozoic conifer plants. It is thefirst family for which detailed morphological, cuticular, andinternal anatomical data have been developed for all of theshoots of the vegetative sporophyte, and both ovulate andpollen producing reproductive organs are characterized for thesame species. Thucydiaceae is the only conifer family knownto produce ovulate fertile zones and compound pollen conesand the first Paleozoic family to display resin canals with anepithelial lining and dissimilar stomatal distribution patternson vegetative and fertile leaves.

Detailed comparisons of T. mahoningensis to previously de-scribed walchians illuminate a number of questions about theappropriateness of traditional approaches to the study of Pa-leozoic fossil conifers and about the adequacy of charactersthat traditionally have been used to define species, genera, andfamilies. It is now clear that walchian species display morevariation in vegetative characters than previously has been ap-preciated. Therefore, detailed data for a wide range of mor-phological, cuticular, and anatomical characters of both veg-etative shoots and fertile structures are required for thedevelopment of useful taxonomic concepts and for the iden-tification of isolated specimens. In some instances, multivariatetests will be required to determine if there are statistically sig-nificant differences in ranges of variation for the characters ofdifferent species. Because characters can show dissimilar pat-terns of variation among the different organs of a species, we

cannot rely primarily on data from only one type of organ(e.g., ovuliferous dwarf shoots) or on one category of data(e.g., cuticular characters) to accurately identify taxonomic en-tities or to infer systematic relationships. Species, genera, andfamilies are most confidently defined by novel combinationsof characters drawn from all organs of the sporophyte.

We anticipate that ongoing studies, like those of growtharchitecture and of quantitative variations in Thucydia vege-tative branch morphology, will further refine our understand-ing of the ranges of variation that can be expected across thevegetative body of a single walchian conifer species. This in-formation will be valuable in deciphering the taxonomic com-position of multispecies assemblages such as those at Hamil-ton, Kansas (Liu et al. 2000) and at many localities throughoutEurope (Florin 1938–1945) and for testing taxonomic hy-potheses of the Permo/Carboniferous walchian conifers fromEurope and North Africa. The last studies are probably themost challenging, but they are also crucial for establishing aconsistent valid nomenclature for walchian taxa, for ultimatelyunderstanding the structure and diversity of ancient coniferspecies, and for allowing workers to confidently identify newlydiscovered walchian conifer specimens. Such studies will dra-matically increase the number of species of well-known wal-chian conifer plants and will provide data that are crucial forresolving the overall pattern of conifer phylogeny.

Acknowledgments

We thank Melissa and Greg McComas for materials col-lecting and Melissa McComas for rendering cuticular and an-atomical preparations. Comparative studies of walchian con-ifers were conducted with the kind assistance of Tom Taylorand Rudy Serbet in Lawrence, Kansas; Jopie Clement-Wester-hof in Urecht; Jean Broutin and Christiane Blanc-Louvel inParis; Yves Lemoigne, George Barale, and Abel Prieur in Lyon;Hans Kerp in Muenster; Manfred Barthel and StephanSchultke in Berlin; Harald Walter in Dresden; Ronni Rosler inChemnitz; Ralf Werneburg in Schleusingen; Zlatko Kvacek,Jurı Kvacek, and Zbynek Simunek in Prague; A. V. Gomankovand S. Naugolnykh in Moscow; Olga Kossovaya in St. Pe-tersburg; Ruben Cuneo and Sylvia Cesari in Buenos Aires;Shaila Chandra and Kamal Jeet Singh in Lucknow; and D. D.Pant and Shonali Chaturvedi in Allahabad. Hans Kerp andRuben Cuneo provided valuable discussions regarding the tax-onomy and nomenclature of Paleozoic conifers. This work wassupported in part by Consejo Nacional de Ciencia y Tecnologia(CONACYT grant 128361 to G. R. Hernandez-Castillo) andthe National Science Foundation (grant DEB-9527920 to G.W. Rothwell and G. Mapes).

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Thucydiaceae Fam. Nov., with a Review and Reevaluation of Paleozoic Walchian Conifers

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