Synonymy Amongst the Arbuscular Mycorrhizal Fungi: Glomus claroideum, G. maculosum, G....

7/25/2019 Synonymy Amongst the Arbuscular Mycorrhizal Fungi: Glomus claroideum, G. maculosum, G. multisubstenum and

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Annals of Botany 82 : 601624, 1998Article No. bo980714

Synonymy Amongst the Arbuscular Mycorrhizal Fungi: Glomus claroideum,G. maculosum, G. multisubstenum and G. fistulosum

CHRI S TOP HE R W ALKER* and MAURI TZ VES TBERG* Biological Research and Imaging Laboratory, 2 Penny Hedge, New Milton, Hampshire BH25 7TB UK and

Agricultural Research Centre of Finland, MTT, Laukaa Research and Elite Plant Laboratory, Antinniementie 1,

FIN-41330 Vihtauori, Finland

Received: 19 March 1998 Returned for revision: 11 June 1998 Accepted: 29 June 1998

Ex-type material ofGlomus fistulosumwas re-established in pot culture and differences from the description in theprotologue noted. Type specimens and other cultures from Europe, and North and South America showed theoriginal species description was incorrect. The species is re-described from pot cultured specimens. The holotype ofGlomus claroideum was also examined. The two species were morphologically identical. This was confirmed bycomparisons with other specimens ofG. claroideum. One culture, used in the protologue, but not designated as aparatype, had smaller spores than those from other G.fistulosumor G.claroideumcultures, but could not otherwisebe separated. They are therefore synonymized. Type material of Glomus maculosum and specimens of Glomusmanihotis from Colombia were studied. The latter came from a heavily parasitized pot culture, and its sporespossessed the maculiferous ornamentation that supposedly characterized the former. Similar structures were notedin the isotype of G. claroideum. The feature is probably environmentally induced and should not be used asa taxonomic characteristic. The conclusion is drawn that Glomus maculosum should also be synonymized withG. claroideum.Glomus multisubstensumis considered from its protologue, and this too should be synonymized withG.claroideum. An epitype is defined to aid in the circumscription ofG. claroideum. Less comprehensive comparisonswere also made with other similar species, G. albidum, G. przelewicense, G. lamellosum, G. pustulatum and G.diaphanum. It is concluded that G.lamellosumis inadequately defined, and its validity as a species needs clarification.It is also suggested thatGlomus albidumand G. przelewicensemay be conspecific.

1998 Annals of Botany Company

Key words:Epitype,Glomus fistulosum,Glomus claroideum,Glomus maculosum,Glomus multisubstensum,G.albidum,G. przelewicense, G. lamellosum, G. pustulatum, G. diaphanum, Glomales, arbuscular mycorrhiza, synonymy,taxonomy.

I N T R O D U C T I O N

During a survey of arbuscular mycorrhizal fungi in Finland,a species was found and established in pot culture from 63locations (Vestberg, 1995). Nineteen of these cultures werestudied in detail, and similar fungi from Scotland, theCzech Republic and Ireland were also examined todetermine whether they were morphologically distinguish-able.

Whilst attempting to identify the Finnish fungi, com-parisons were made with existing descriptions of membersof the Glomales, and it was at first thought that theyrepresented a taxon new to science. However, species

descriptions of fungi in the Glomales are sometimesinaccurate or incomplete, and the type material of speciesthat might be similar to our fungi were examined wherepossible.

Included in this examination was the culture from whichthe type material of the fungus Glomus fistulosum Skou &Jakobsen was derived. The specimens from this culture hadcharacteristics at variance with the description in the

* E-mail walkerglobalnet.co.uk For correspondence. E-mail Mauritz.VestbergMTT.Fi

protologue (Skou and Jakobsen, 1989), so we examined theholotype material to satisfy ourselves that the type cultureremained uncontaminated by other species ofGlomus, andthat our interpretation of the morphology was correct.

Spores from cultures of fungi assigned to the speciesGlomus claroideum Schenck & Smith were also examined,since the diagnostic characteristics of that species (Schenkand Smith, 1982) fitted the morphological characteristics ofG.fistulosum, though not its original description. Similarly,the species Glomus maculosum Miller & Walker was re-examined because it shared some characteristics (Miller andWalker, 1986) with the aforementioned species. A culture ofGlomus manihotis Howeler, Sieverding & Schenck from

Colombia, showing some of the characteristics ofGlomusmaculosum, was examined to compare it with the otherfungi we had studied. Spores of Glomus przelewicenseBaszkowski were examined from the type material, sincethe description and illustrations in its protologue(Baszkowski, 1988) also bore some similarity to that ofG.claroideum. Specimens ofGlomus multisubstensumMukerji,Bhattacharjee & Tewari were not available for examination,but its species description (Mukerji, Bhattacharjee andTewari, 1983) was studied for comparison with the abovespecies. Other similar species,G.albidum Walker & Rhodes,

0305-73649811060124 $30.000 1998 Annals of Botany Company


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602 Walker and VestbergGlomus claroideum Emended

G.lamellosumDalpe, Koske & Tews, G. pustulatumKoskeet al., and G. diaphanum Morton & Walker were alsocompared.

The taxonomic system of wall structure originally definedby Walker (1983) and later extended by Berch and Koske(1986), Morton (1986), Spain, Sieverding and Schenck(1989) and Walker (1986), was intended only as an artificialsystem to be used in species description (Walker, 1992),regardless of misrepresentative statements to the contrary(Bentivenga and Morton, 1995; Stu rmer and Morton,1997). As such, it is useful for the purposes of comparingand cataloguing the fungi in the Glomales, but is not solikely to be adequate for providing information abouthomologous developmental characteristics. Nevertheless, ithas provided a solid base for critical examination of sporesof arbuscular mycorrhizal fungi, and pending a fullyscientific evaluation of the wall components in the group,will continue, perhaps with further amendments, to beuseful in species descriptions. We therefore have maintainedits use, with slight modification, in the following speciesdescriptions. We have substituted the functional term

flexible (Morton, 1995) for membranous (Walker, 1983).Although the taxonomy of the Glomales is based mainlyon light microscopy of intact or lightly crushed spores, thereare fundamental difficulties in their study. The compoundmicroscope is intended for observation of thin sections.The depth of focus is limited, and it is often possible to viewsuch sections without serious artefacts. Interpretation of theimageis consequently relatively straightforward. In contrast,examining relatively large objects such as spores ofarbuscular mycorrhizal fungi, is subject to many problemscaused by refraction and refringence, resulting from theirshape and thickness. Interpretation of the image musttherefore be carried out with these limitations in mind.

M A T E R I A L S A N D M E T H O D S

Fungal isolation

Open pot cultures (Gilmore, 1968) were produced overseveral years in various ways. Most of the cultures used wereproduced from more than one spore, and thus cannot beunquestionably assigned to a single genet. Only culturesproduced from a single spore are described as isolatesbecause the use of more than one spore as inoculum canproduce a culture originating from more than one ortet(Walker, 1992). Nevertheless, with three exceptions, an ex-type pot culture ofGlomus lamellosum, an un-purified potculture from field soil and a contaminated pot culture of

Glomus mosseae, only one morphotype of spore wasproduced in each culture. In addition to the pot-culturedspecimens, some spores obtained directly from field soilwere examined.

Specimen preparation

Sporeswere extractedfrom thesoil or potculture substrateby centrifugation and sugar flotation (Walker, Mize andMcNabb, 1982) or by wetsieving anddecanting (Gerdemann

and Nicolson, 1963). Specimens were then selected andplaced in a dish of water for examination under thedissecting microscope at magnifications up to 50 withillumination by incident light from a fibre-optic quartz-halogen light source with a colour temperature of 3200 K(Walker, Gianinazzi-Pearson and Marion-Espinasse, 1993).

Record maintenance

Details of original collection and isolation, resultantcultures and subcultures, and herbarium specimens (Tables1 and 2) have been recorded in a database developedspecifically for the purpose. Original soil or plant samplesare given a unique registration number. Each culture pot isgiven an Attempt number (unique to each culture attemptmade from any one original sample) and culture number(sequential for sub-cultures from a successful attempt).Information about cultures and field collections from anycollection can be entered into the database, hence attemptand culture numbers do not necessarily indicate that wehave maintained the culture ourselves. Semi-permanent

microscope slides and, where available, spores in either 5%formaldehyde or 0025% aqueous sodium azide solution,were kept. Voucher specimens of all fresh material havebeen accessed into the personal herbarium of the firstauthor, each individual collection being given an accessionnumber (W number). Voucher numbers may have beengiven to specimens borrowed from other collections (e.g.from a herbarium) and subsequently returned. For example,the culture from which the type material Glomus claroideumwas obtained was designated Attempt 6223, (Attempt 622,Culture 3) and the two samples examined from it wereaccessed as W947 and W2955. The former was a samplereceived directly from Dr N. C. Schenck, whereas the latterwas the holotype loaned by the curator of Oregon State

University (OSC). The three subcultures of Glomusfistulosum examined in most detail for this study wereAttempts 56 (herbarium specimens W1779 and W1840),58 (W1841), and 519 (W2844). Further details of thedatabase,whichis availableby arrangement,can be obtainedfrom the first author.

Morphological features

For some of the fungi, taxonomic features were studiedfrom both young (14 weeks) and old (44 weeks or more)growing cultures, allowing observation of developmentalsequences in spore wall components and changes in colour

with advancing age, although no formal experimentalapproach was taken to sequencing the spore development.For others, only mature cultures, or cultures of unknownage, were available. Spores extracted from dried orrefrigerated pot culture substrate were also examined forsome cultures. Spores were examined in water (Spain, 1990),in polyvinyl alcohol lacto-glycerol (PVLG) (Omar, Bollandand Heather, 1979) and PVLG with Melzers reagent, 5:1vv (PVLGMelzers) (Walker et al., 1993) through acompound microscope with bright field and Nomarskidifferential interference contrast illumination. Spore


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Walker and VestbergGlomus claroideum Emended 603

T

1.Geographicandc

ulturinginformationforspecimenso

fGlomusfistulosum

examinedina

comparatiestudyofsimilarspeciesinthearbuscular

mycorrhizalgenusGlomus

Attempt

culture

Voucher

Cult

uresandlocation

Originalculturemethod

Original

collector

Other

identifier

and

notes

Town

Countr

y

Continent

54

W1498

Jako

bsen,

Denmark

Multisporefr

omsoil

Jakobsen

No.21Ex-type

Askovlermark

Denma

rk

Europe

54

W1579

Jako

bsen,

Denmark

56

W1779

Walker,

Scotland

56

W1840

Walker,

Scotland

57

W1759

Vest

berg,Finland

58

W1841

Walker,

Scotland

59

W2371

Walker,

Scotland

510

W2427

Walker,

Scotland

510

W2780

Walker,

Scotland

512

W2835

Merryweather,

England

517

W2837

Merryweather,

England

519

W2844

Vest

berg,Finland

431

W2374

Walker,

Scotland

Soiltrap

Walker

Foul1

EastNewton

UK

Europe

743

W1853

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V14b

Karsamaki

Finland

Europe

792

W2115

Vest

berg,Finland

Vestberg

V128

Laukaa

Finland

Europe

793

W1843

Vest

berg,Finland

794

W2027

Walker,

Scotland

796

W2269

Gianinazzi-Pearson,

France

2230

W1520

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V92

Narpes

Finland

Europe

2231

W2110

Vest

berg,Finland

2233

W2111

Vest

berg,Finland

2693

W2871

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V151

Korpilahti

Finland

Europe

2712

W1628

Gryndler,CzechRepublic

Multisporefr

omsoil

23A

NovyBydzov

CzechRepublic

Europe

2714

W1688


2715

W1842

Walker,

Scotland

2715

W1912

Walker,

Scotland

2715

W2029

Walker,

Scotland

2717

W1839


27111

W1947

Gianinazzi-Pearson,

France

3132

W1972

Vest

berg,Finland

1rootfragmentmultispore

Vestberg

V112a

Orivesi

Finland

Europe

3132

W2020

Vest

berg,Finland

3134

W2902

Vest

berg,Finland

3353

W1872

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V13

Kuhmo

Finland

Europe

3833

W2849

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V170

Petajavesi

Finland

Europe

4201

W2112

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V138

Jamsa

Finland

Europe

4210

W2113

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V107

Uurainen

Finland

Europe

4221

W2114

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V127

Laukaa

Finland

Europe

4353

W2850

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V174

Jyvaskylan

maalaiskunta

Finland

Europe

4803

W2851

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V184

Jamsa

Finland

Europe

5643

W2370

ON

eill,

Ireland

Soiltrapmu

ltispore

ONeill

Irish.UCDI

Ardattin

Ireland

Europe

6323

W2840

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V12

Nurmes

Finland

Europe

6343

W2852

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V187

Jamsa

Finland

Europe

6353

W2853

Vest

berg,Finland

Soiltrapmu

ltispore

Vestberg

V198

Korpilahti

Finland

Europe


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T

2.Geographicandcu

lturinginformationforspecimensofGlomusspp.examinedincomparison

toGlomusfistulosuminastudyofsimilarspeciesinthe

arbu

scularmycorrhizalgenusGlomus

Attempt

culture

Voucher

Culturerandlocation

Originalculturemethod

Original

collector

Otheridentifierand

notes

Town

Country

Continent

Originallyassignedspeciesname

SpecimensofGlomusclaroideum

576

W1404

Campru

bi,Spain

Unknown

Unknown

Unknown

Scotland

Europe

577

W1467

Walker,

Scotland

579

W2466

Walker,

Scotland

1052

W2709

Walker,

Scotland

Soiltrap

Baszkowski

Leba

Poland

Europe

1932

W1871

Rosendahl,Denmark

Unknown

Rosendahl

Unknown

Denmark

Europe

1934

W2417

Rosendahl,Denmark

1938

W2499

Dodd,E

ngland

1939

W2721

Walker,

Scotland

2511

W2839

Merryweather,

England

Soiltrapmultispore

Walker

EastNewton

Scotland

Europe

2511

W2847

Merryweather,

England

4740

W388

Daft,Sc

otland

Potculturecontaminant

Dundee

Scotland

UK

5975

W2503

Morton,

USA

Potculturecontaminant

Skipper

Clemson

USA

NorthAmerica

5976

W2504

Merryweather,

England

5976

W2846

Merryweather,

England

Authenticated

5985

W2506

Bentivenga,

USA

Unknown

MingLin

Campinas

Brazil

SouthAmerica

5986

W2507

Merryweather,

England

5986

W2845

Merryweather,

England

6223

W947

Schenck

,USA

Unknown

Schenck

Isotype

Sanford

USA

NorthAmerica

6223

W2595

Schenck

,USA

Holotype

None

W538

Fieldco

llected

Fieldcollection

Koske

Koske432

AssateagueIsland

USA

NorthAmerica

None

W1149

Fieldco

llected

Fieldcollection

Walker

Roslin

Scotland

Europe

None

W2191

Fieldco

llected

Fieldcollection

Walker

Tabernas

Spain

Europe

None

W2984

Fieldco

llected

Fieldcollection

Walker

Burascund

India

India

SpecimensofGlomussp.

(W2494)

128

W2494

Walker,

England

Planttrapsinglespore

Newsham

lemchrome

Mildenhall

England

Europe

SpecimensofGlomusmaculosum

4910

W505

Miller,USA

Soiltrap

Miller

Isotype

SturgeonBay

USA

NorthAmerica

4910

W568

Miller,USA

Ex-type

4911

W531

Miller,USA

Soiltrapmultispore

Ex-type

4912

W765

Miller,USA

Soiltrapmultispore

Ex-type


5/24


SpecimensofGlomuslamellosum

2443

W1707

Dalpe,C

anada

Unknown

Dalpe

Ex-type

WasagaBeachProvincial

Park

Canada

NorthAmerica

2444

W2117

Walker,

Scotland

2445

W2392

Dodd,E

ngland

2444

W2432

Walker,

Scotland

2446

W2712

Walker,

Scotland

2446

W2868

Walker,

Scotland

4720

W385

Daft,Sc

otland

Unknown

Daft

Culturecontaminant

Dundee

UK

Europe

SpecimensofGlomuspustulatum

3680

W2066

Walker,

Scotland

Soiltrap

Walker

Hallside

Cambuslang

Scotland

Europe

None

W655

Fieldco

llected,

USA

Fieldcollection

Koske

Isotype.Koske534

MoonstoneBeach

USA

NorthAmerica

None

W1064

Fieldco

llected,

USA

Fieldcollection

Friese

Isotype.Friese33

MoonstoneBeach

USA

NorthAmerica

SpecimensofGlomusmultisubstensumconsideredfromprotologuedescription

only

None

None

Fieldco

llected,

India

Fieldcollection

Bhattacharjee

Holotype.DUKMB

500

Delhi

India

India

SpecimensofGlomusalbidum

2881

W79

Rhodes,

USA

Multisporefromsoil

Rhodes

Ex-type

WashingtonTownship,

OhioUSA

NorthAmerica

2881

W169

Rhodes,

USA

Isotype

2881

W170

Rhodes,

USA

Ex-type

2884

W258

Walker,

USA

Ex-type

4560

W282

Sanders,

England

Soiltrap

Sanders

Bramham

England

Europe

None

W179

Fieldco

llected

Fieldcollection

Walker

Paratype

Rhodes

USA

NorthAmerica

SpecimensofGlomusprzelewicense

None

W2957

Fieldco

llected,

Poland

Fieldcollection

Baszkowski

No.

578

Przelewice

Poland

Europe

SpecimensofGlomusmanihotis

6270

W2828

Dodd,U

K

Multispore

Dodd

Colombia

Unknown

Colombia

SouthAmerica

SpecimensofGlomusdiaphanum

6410

W949

Multispore

Morton

Morton73

Elkins

USA

NorthAmerica

6410

W952


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measurements were made from newly made microscopeslides of spores in PVLG. Spore colour was determinedunder the dissecting microscope from spores suspended inwater. Colours were matched by name and number [e.g.sienna (11)] with a colour identification chart (Anon, 1969)illuminated simultaneously with a split fibre optic from thesource used to illuminate the spores. The paler colours onthe chart lack names, so they have been assigned thefollowing: 1, white; 2, ivory; 3, pale yellowish cream; 4, palepinkish cream; 5, yellowish cream; 6, pale ochraceous; (7,white, repeated); 8, ochraceous; 9, ochre.

Description of spore wall structures follow the con-ventions of Walker (1983) with some modification toaccommodate recent arguments about the nature of sporewall components. There has been much discussion about theuse of the terms wall and wall layer in the taxonomy ofthe arbuscular mycorrhizal fungi (Berch, 1986; Walker,1992; Stu rmer and Morton, 1997), stimulated by theinability to define with certainty the true nature of the sporein the Glomales. It is unlikely that all the spore types formedby members of this order are homologous. Some may

indeed be simple asexual spores, whereas others are verycomplex in structure, and may be sporangia or sexualstructures. Until this controversy is resolved, it can be nomore correct to use one term than the other. We havetherefore chosen to use the term component, as a neutralchoice, when describing the elements of wall structure inglomalean spores, and to retain the use of the term groupwhen one or more of these components separate into anassemblage in crushed spores on microscope slides.

Measurements of spore dimensions were made witheyepiece graticules calibrated with a stage-micrometer. Forstatistical analysis, it is necessary to prevent bias in selectingspecimens for measurement. To achieve this, the sporeswere extracted and placed in a dish of water under a

dissecting microscope. The dish was marked into squarescorresponding with the field of view at 50magnification,and scanned systematically from top left to bottom right.All spores in each field were picked out and placed in awatch glass of water. They were then transferred, with apipette or fine forceps, to microscope slides. The slides werescanned in a similar manner to the dishes until 100 had beenmeasured, so that no biased selection of specimens couldtake place. For a few of the samples, more than 100 sporeshad been measured during previous work. In these instances,the entire set of measurements was taken and randomobservations were deleted until 100 remained. Some sampleswere of fewer than 100 spores. These, and the data excludedfrom sets of more than 100 measurements, have been

included in general consideration of the species and indetermination of maximum and minimum spore dimensions,but have not been used in statistical analysis. At least one setof measurements was made for each attempt examined, andin some instances, two or three samples were measured,either from the same, or from different cultures. Theconvention that length includes all spore wall components,and is measured perpendicular to the spore base (subtendinghypha) is followed (resulting in the possibility of sporesbeing broader than long). The width is taken as a lineacross the broadest point at right angles to the length.

Reaction to Melzers reagent

The reaction of the spore wall components to PVLGMelzers was routinely assessed when fresh specimens wereprepared on microscope slides. By the nature of pot cultures,most of these were from mature spores, although someimmature spores were inevitably also included. An ex-perimental approach was taken for Glomus fistulosum:100fresh and 100 dry spores from each of five cultures weremounted in PVLGMelzers and individually examined.

Germination characteristics

Germination characteristics were noted, where infor-mation was available, from the protologues and otherpublished descriptions. In addition, where germinatingspores could be seen in other collections, their characteristicswere noted. In an experimental assessment, spores (fromAttempt 627 in Vestbergs database) were retrieved fromair-dried pot culture substrate which had either been storedat 8 C (three trials), or had been frozen to 20 C (six

trials) for 2 or 6 weeks. Those spores that had been frozenwere gradually thawed at 4 C for 24 h, after whichapparently healthy spores were selected under a dissectingmicroscope, surface disinfested for 2 min in 05% NaOCl,and washed in three changes of sterile water. Excess liquidwas then absorbed on sterile filter paper, and the sporeswere transferred to 15% Difco water agar (pH 55), andincubated in darkness for up to 8 weeks. The number ofspores used in different trials varied between 16 and 40.Spore germination recording began 7 d after starting theincubation. For observation of germination characteristicsand for photography, germinated spores were stained inlactophenol-methyl blue.

Specimens examined

All the species currently described in the genus Glomuswith species descriptions similar to that of G. fistulosumwere considered. Where possible, specimens, both preservedmaterial and fresh cultures, were examined, and comparedwith their protologues and withG.fistulosum. Some specieswere unavailable as specimens, and so they are consideredsolely from their descriptions. As well as the fresh materialspecifically produced for this study, relevant preservedmaterial in Walkers personal herbarium was included(Tables 1 and 2).

Glomus fistulosum Skou & Jakobsen. Mycotaxon 36,274 (1989)

The holotype ofGlomus fistulosum (Attempt 54) wasstudied at the herbarium of the University of Copenhagen.It consists of microscope slide preparations, from potnumber 21, a multi-spore culture from the AgriculturalResearch Department at the Ris National Laboratory,Denmark (Skou and Jakobsen, 1989). No voucher numberwas given to this collection. In addition to the type material,12 samples from nine different ex-type subcultures (including


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two from the type pot culture itself) were examined (Table1).

Two cultures assigned to this species were donated bycolleagues. One, from the Czech Republic, was establishedby inoculating a host plant in sterile substrate with 20morphologically similar spores from soil (Gryndler, 1995).From this culture, seven samples from a total of five potcultures were examined (Table 1). A sample from an Irishisolate (W2370) started with a single-spore from a treenursery soil trap, was studied from a closed pot culture(Walker and Vestberg, 1994). One other sample of G.

fistulosum(W2374) was examined from a mixed-species soiltrap (Attempt 431) from a site in Scotland.

All except one of the 21 Finnish arbuscular mycorrhizalfungi (Table1) were baited out in open pot culture (Vestberg,1995) by mixing soil from the field with a sterile substrate ina pot, and sowing with a suitable host (soil trap culture).This was followed by establishment as a single-taxon cultureby extracting spores from the pots which were then placedwitha suitable host in sterile substrate (multi spore cultures).The exception, Attempt 3132 was produced by inoculating

a mycorrhiza-free host plant with a single root fragment. Amulti spore culture was subsequently made from theresultant pot culture, producing samples W1972 and 2020.The fungus has been recorded as mycorrhizal with a largenumber of plant hosts.

Glomus claroideum Schenk & Smith. Mycologia 74, 84(1982)

Among the samples of Glomus claroideum examined(Table 2), were an isotype sample (W947, from Dr N. C.Schenck) and the holotype W2595 (OSC accessionnumber 40252), loaned by the herbarium of Oregon StateUniversity. The spores of W2959 were either preserved in

lactophenol, or had been mounted on lactophenol slides.The slides had dried out and were re-made with PVLG. Inaddition, new PVLG-mounted slides were made from thelactophenol-preserved material. All living material of thisculture seems to be lost, so another culture was obtainedfrom Dr J. Merryweather, University of York, UK (driedinoculum of INVAM SC186; W2503) later examined froman active pot culture (UY1053, W2504 and W2846). Thisfungus was specifically mentioned in the protologue, but notformally designated as a paratype. Although lacking anyformal taxonomic status, by merit of its special mention inthe protologue, this isolate provides living evidence of thespecies as conceived by Schenck and Smith (1982). Thisfungus originated as a pot culture contaminant from South

Carolina, and was first cultured by Dr H. Skipper, ofClemson University, North Carolina.

Another organism found contaminating a pot culture ofGlomus mosseae (Nicolson & Gerdemann) Gerdemann &Trappe contributed by Dr M. J. Daft, University ofDundee, UK (W388), was found to fit the description ofG. claroideum.

A second culture was provided by York University, bothas dried inoculum from INVAM (BR-147A, W2506) andfrom the substrate of an active pot culture (UY1052, W2507and W2845). This fungus, which originated from Brazil, and

Skippers North Carolina culture, were used in a recentinformal re-description ofGlomus claroideum(Stu rmer andMorton, 1997).

Two cultures had origins in Scotland. Attempt 57 came,via Rothamsted Experiment Station, to Cabrils, Spain(contributed by Dr A. Camprubi). Other than that itoriginated from peat (pH 60) from a hillside in Scotland,nothing else is known about this culture. Two cultures ofthis fungus were examined, represented by the voucherspecimens W1404 and W2466. The second Scottish culture,made and purified by Dr J. Merryweather as UY73, wasproduced from a sample taken near the type locality ofScutellospora calospora (Nicolson & Gerdemann) Walkerand Sanders, at Denhead of Foulis, Perthshire. Specimenswere studied from an original soil trap (W2839) and asubsequent multi-spore, single-species culture (W2847).

Another culture of G. claroideum was provided fromDenmark by Dr S. Rosendahl, but without details of itsorigins or culturing history. Four different subcultures ofthis were examined. Specimens were retained as W1871,W2417, W2499 and W2721. Another mainland European

culture from a Polish soil trap culture established by Dr J.Baszkowski was studied (W2709).In addition to the cultured samples, four field collections

yielded specimens ofGlomus claroideum. One, which camefrom Assateague Island, Maryland, USA, was donated byDr R. E. Koske (W538). Two were from Europe (Scotland,W1149 and Spain, W2191), and the fourth was from India(W2894). Mycorrhizas are formed with a large range of hostplants.

Glomus maculosum Miller & Walker. Mycotaxon 25,218 (1986)

As with G. claroideum, no living material of the soil traptype culture or the multi-spore subculture ofG.maculosumcould be found, but preserved material (W505) of theisotype and ex-type sub-cultures (W531, W568 and W765)(Table 2) was examined. Locating living material of thesecultures proved impossible; they were apparently lost fromIowa State University and the INVAM collection in Florida.This fungus, originally cultured from an apple orchard inWisconsin, USA has been grown in pot culture with Malusdomestica, Sorghum sudanense and Coleus x hybridus.

Glomus lamellosum Dalpe, Koske & Tews. Mycotaxon43, 289 (1992)

Six samples from among four ex-type cultures (Table 2)(with Allium porrum) of G. lamellosum (W1707, W2117,

W2432, W2392, W2712 and W2868) were examined. It isnot known if the original culture was from a soil trap or apurification through selected spores.

Glomus pustulatum Koske, Friese, Walker & Dalpe.Mycotaxon 26, 143 (1986)

Two voucher collections of this were examined. One wasfrom Koske (W655) and the other by Friese (W1064) on thesame day. Later enquiries revealed that these were from thesame sample, and they were both subsamples of the isotype.


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The species was also found and pot-cultured in Canada, butwe have not seen specimens. It was also recovered from asoil trap pot culture (Plantago lanceolata L.) started from anold coal mine spoil heap in Cambuslang, Scotland (W2066).In addition to being symbiotic with P. lanceolata, thisspecies is known, from the paratype, to form arbuscularmycorrhizas with Lathyrus maritumus (Koske et al., 1986).

Glomus multisubstensum Mukerji, Bhattacharjee &Tewari. Transactions of the British Mycological Society81, 3 (1983)

No specimens were available for examination. Enquiriesof the herbarium at Delhi (DU), and of Drs Mukerji andTewari have revealed that the type material has been lostand no ex-type culture can be found. The protologue wasused to study the characteristics of this fungus, which wasreportedly mycorrhizal with Zea mays (Mukerji et al.,1983).

Glomus albidum Walker & Rhodes. Mycotaxon 12, 509

(1981)

As with so many of the valuable cultures from the past, allknown ex-type pot cultures have been lost or discarded.Cultures existed at Iowa State University, Ohio StateUniversity and INVAM, Florida, but none could be locateddespite repeated enquiries. Consequently, only preservedspecimens have been examined. Four samples of the originaltype culture [W79, W169 (isotype), W170 and W258] werestudied. Two other collections, one from a field collection inIowa, USA (W179), and one from a soil trap culture fromYorkshire, England (W282) were examined (Table 2). Thefungushas been grown in symbiosis with Zeamays, Sorghumulgare and Populus x euramericana.

Glomus przelewicense Baszkowski. Bulletin of the PolishAcademy of Sciences. Biological Sciences 36, 272 (1988)

The holotype collection, consisting of 20 microscopeslides, was kindly made available for examination by Dr J.Baszkowski. All except one (which had two spores) of theslides, contained only a single spore mounted in PVLG. Itis known only from a field collection of soil beneath Thujaoccidentalis (Baszkowski, 1988).

Glomus diaphanum Morton & Walker. Mycotaxon 21,433 (1984)

Isotype (W949) and ex-type (W952) material from theoriginal soil trap culture with Sorghum sudanense wasstudied from existing microscope slides in polyvinyl alcohollactophenol (PVL). No fresh material was examined.

Glomus manihotis Howeler, Sieerding & Schenck inSchenck et al. Mycologia 76, 695 (1984)

A sample of a multi spore culture (host unknown) fromColombia was provided by Dr J. C. Dodd, InternationalInstitute of Biotechnology, Canterbury, Kent, UK. At first,

it was thought that this was an example ofG. maculosum,but later examination showed it to be a heavily parasitizedG.manihotis(W2828). It is included in this study (Table 2)because some of its characteristics cast light on to thecomparison ofG. maculosumwith G. claroideum.

R E S U L T S

Colour

In general appearance, the spores of G. fistulosum, G.claroideum and G. maculosum (except for the spottedappearance of older spores) differ only slightly (Figs 15),and there was as much variation within cultures as amongthem. Their appearance also changed over time with storagein different preservatives, mainly because of changes incolour and degradation of the outer wall components.

In the protologue, the colour of the spores ofG.fistulosumwas described as pale yellow, and no mention is made ofvariation. Colours of stored and fresh specimens from theex-type cultures in Attempt 5 of G. fistulosum varied, but

could loosely be described as shades of yellow. The palestspores were ivory (2), and the darkest normally ochre (9),though in one sample they were pale apricot (pale 47). Theyalso varied with time of storage, gradually becoming muchdarker once detached from their living host. For example,samples from Attempt 519 were uniformly straw (50) incolour, even after 9 d in water at room temperature, butafter a further 9 d, they varied between straw and ochraceous(8). Colour of other isolates assigned to G. fistulosum alsovaried (Table 3), but still within a broad definition ofvarious shades of yellow, and with the palest being ivory (2)and the darkest usually ochre (9), but occasionally apricot(47).

Because the spores in the type material ofG. claroideum

have been preserved in lactophenol they have discoloured.No culture of this isolate could be located to determine thecolour of living spores. The protologue describes them ashyaline to yellow, becoming yellow-brown with age,but no reference is made to any colour standard. This rangeis consistent with our observations, in which we found thespores to be (rarely) hyaline or white (1), and normallyvarious shades of yellow, from ivory (2) to pale yellowishcream (3) to ochre (9) through yellowish cream (5) to paleochraceous (6) to ochraceous (8).

The colour ofG. maculosum spores from different samplesof the same culture was not consistent. However, those fromAttempt 4910 [yellowish cream to pale ochraceous toochraceous (568)], were assessed after storage in 5%

formaldehyde solution. Attempt 4911, assessed fromfreshly extracted spores, was pale straw (50) to ochraceous(8), but both results can be broadly interpreted as variousshades of yellow.

The protologue ofG.lamellosumgives the colour of thesespores as hyaline (when young), lemon yellow to lightyellow at maturity (No. 86 on the ISCC NBS Color NameCharts), equivalent to between yellowish cream and paleochraceous (5 and 6) on the RBG chart. One of the samples,W385 (the pot culture contaminant from Attempt 4720),was recorded only as an unmatched colour, pale yellow. The


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first ex-type sample (W1707, Attempt 2443), had sporesthat were ivory (2) when young, and pale ochraceous toochraceous (68) at maturity. A sample W2117, fromAttempt 2444 had yellowish cream to straw (550) spores.Spores(W2432) from thesame potculture almost a year laterwere white to yellowish cream to pale ochraceous (156).Two more samples of this fungus, both from Attempt2446, were assessed. In the first, W2712, in which sporeswere described as hyaline to pale yellow, no chart was used.Specimens from a later sample, W2868, were ivory, paleochraceous, ochraceous, or, rarely, ochre (2689).

We have not seen fresh spores ofG.pustulatum, but theyare described in the protologue as pale yellow to yellow-brown or orange-brown, though no chart was used toprovide colour matching. Similarly, there was no freshmaterial of G. multisubstensum available for examination.Its spores are described as light brown, and the wall layersas brown or pale yellow brown in the species description.

No colour chart matching was carried out on livingmaterial ofG.albidum, but from original records spores arehyaline when young, white to off-white at maturity,

appearing yellowish to brownish yellow by transmittedlight. This colour is maintained in samples preserved in 5%formaldehyde solution.

According to the original species description, spores ofG.przelewicense are yellow (2.5Y 88), equivalent to ochra-ceous on the RBG chart. In the original description,Blaszkowski describes a darkening of the colour to reddishyellow (5YR 66) when viewed through a compoundmicroscope. A similar characteristic was recorded for G.albidum (Walker and Rhodes, 1981). Spores ofG. diaphanumare consistently hyaline, in contrast to all fungi studied here,which, whilst sometimes being hyaline when immature, arepigmented at maturity.

Spore dimensions

For G. fistulosum mean spore dimensions ranged widely(Table 4, Figure 29), but generally could not be separatedstatistically when considered as a group (Table 5). Bothlength and width measurements for two different samples ofG.fistulosumfrom the Czech Republic (Attempts 2715 and2717) were significantly different (P005). Sizes of sporesin G. fistulosum are given as 6722078200 m in theprotologue, and from our studies this can be modifiedslightly, including the protologue measurements to 6022060243 m.

The size range ofG. claroideum is quoted as 70180 m

diameter (mean 130) when globose, and5912672145 mwhen subglobose to irregular. Our measurements of typematerial (n34) 9517592205 (mean 130133), and(n100) (63)81181(51)86188 (mean 129130) m,extend the maximum spore dimensions somewhat. Stu rmerand Morton (1997) give a size range of (100)120140(180) m diameter, falling within our new range, buterroneously implying that the spores are all globose. Manyspores had an apparent break in development of laminatedwall component, giving the impression of two separatelaminated components. Our other measurements (Table 3)

result in a composite measurement of 6319970226 m.Spores of the type are globose to subglobose, with aremarkably narrow size range and little variation. Of 100measured spores in the holotype, W2595, 74 were globose,13 broader than long, and 13 longer than broad. A numberof spores (11 out of 100) had two subtending hyphae.

Spore dimensions of G. maculosum have the range(95)102178 (220)(95)102178 (220)m. This isslightly changed from the protologue as a result of newmeasurements. From 100 spores of W505, the mean is138139 m. The subtending hypha behaves in the sameway as that of the G.claroideumand G. fistulosumculturesexamined.

In the protologue, dimensions ofG. lamellosumspores aregiven as (98)106142122162 m. Measurements of 100spores from an ex-type culture (W2868 from Attempt2446) resulted in the dimensions of 8416081174 (mean219174) m extending the upper range somewhat. Thevolunteer specimen from a pot culture in Scotland, W385,was 10010782169 (mean 130131) m.

The spore sizes for G. pustulatum are quoted as (43)

86140

(60)86140 m in the protologue, and no othermeasurements are available. Glomus multisubstensum, alsofrom the protologue only, has spore dimensions of 100150 m, which are within the dimensions ofG. claroideum.Dimensions in the protologue of G. albidum are given as(85)95168 (198)(85)95168 (177) m. Newmeasurements on preserved material extend the lower rangesomewhat, resulting in (68)95168 (198)(50)95168(177) m. All spores in type of G. przelewicense arecrushed, and consequently cannot be re-measured. They aredescribed in the protologue as mostly globose to subglobose,(120)137 (160) m diameter, or ovoid and 160100 m.The spores ofG. diaphanum are mainly globose, but can alsobe ellipsoid, particularly in roots. Their dimensions, com-

bined from the species description are (36)7486(39)64(132) m.

Wall structure

The wall structure of the ex-type material ofG. claroideumand G. fistulosum did not correspond with the originalspecies description, though the fistules, used to characterizethe latter, were evident in moribund spores of both species.

The spores of G. fistulosum have a muronym (Walker,1986) of A(EL)B(F), which is much simpler than thatoriginally described. The innermost wall component isunitary, though its flexibility and consequent collapse and

folding in the mounting medium can give an erroneousimpression of multiple layering, and in many specimens iscompletely separated from the other wall components (Figs1921). In contrast, the wall structure description of G.claroideum is slightly more complex than described, beingthe same as G. fistulosum. Because of its age and state ofpreservation, the evanescent component can be detectedonly from remnants, and the innermost, flexible componentis quite difficult to see (Fig. 11). The laminations have, onsome specimens, separated to give an erroneous impressionof multiple laminated components (Fig. 9). On those few


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F15. Spores in a dish of water, all at the same magnification. Unless otherwise stated, the samples are freshly extracted from a pot culture.The epithets in the legends are those used when first identified. Fig. 1. An ex-type sample ofGlomus fistulosum. Fig. 2. Part of the holotype ofG.claroideumafter preservation in lactophenol. The preservative has caused considerable darkening of the specimens. Fig. 3. The culture of G.claroideumfrom South Carolina relied on in a partial redefinition of the species by Stu rmer and Morton (1997). Fig. 4. A Brazilian culture ofG. claroideum, also used by Stu rmer and Morton (1997). Fig. 5. Part of the isotype ofG . maculosum after preservation in 5% formaldehyde

solution.


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spores where the subtending hypha can be seen, this flexiblestructure is completely separate from the subtending hypha,although it may bulge into it. For the living specimens ofG.claroideum, the wall structure of the spores had a muronymof A(EL)B(F) in all specimens examined. Studying theliving cultures, we found the mature wall structure to be ofthree or four components (depending on interpretation) intwo groups. The first group (group 1), which forms the mainstructure of the spore, consists of one thin, hyalinecomponent that disappears as the spores age (designated Ein the muronym), and a thicker, pigmented, laminatedcomponent (L). The evanescent component may also bepartly covered by a mucigel-like substance, interpreted byStu rmer and Morton (1997) as a layer of the outermost wallof the spore, but on our specimens this is a rare occurrence.This (and the evanescent component) may or may not bepresent on both immature and mature spores, and we donot consider that the evidence is sufficiently strong toascertain whether it is really part of the wall structure, or anexudation similar to that produced in G.iscosumNicolson(Walkeret al., 1995). It is unlikely that light microscopy will

be capable of resolving this, and its clarification willprobably require ultrastructural examination of spores,subtending hypha and sporogenous mycelium. The secondgroup is a single, flexible component which does not appearlayered under the light microscope. In the freshly extracted,living material, it is easier to observe the manner of itsformation than in preserved, fixed specimens. It appears tobe produced only after completion of group 1, and by light

F. 6. Spores produced sparsely in the cortex of a root from an ex-type pot culture of G. fistulosum.

F78. Spore formation from two subtending hyphae. Fig. 7. Two adjacent subtending hyphae from an ex-type pot culture ofG. fistulosum.Fig. 8. Two opposite subtending hyphae from the isotype ofG. claroideum.

F912. Wall structure ofGlomus claroideum(911 from the isotype). Fig. 9. Separation (arrow) of the layers in the laminated wall componentgiving the erroneous impression of two separate components. Fig. 10. Early development of the inner, flexible wall group (wall component 3)(arrow). Fig. 11. A later stage in development. Wall component 3 (arrow) is fully developed and thickened, and, despite the specimen beingcrushed, remains close to the laminated component as would normally be the case in an intact spore. Fig. 12. A young spore ofG.fistulosumfromFinland showing all three wall components (1, 2 and 3). Group B, consisting of component 3, has separated from the laminated structural

component of wall group A.

F1314. Formation of internal maculae. Fig. 13. A spore from the G.maculosumisotype, showing the maculae from which it was named. Fig.14. A spore of the G. claroideum isotype, showing structures identical to those used to define G. maculosum.

F1517. Subtending hyphae ofG. claroideum and spores originally identified as G. fistulosum. Fig. 15. An immature spore, from Finland,showing the persistent subtending hypha (arrow). Fig. 16. A mature spore ofG.claroideum(from the isotype) showing the normal considerablereduction of subtending hypha (arrow). Fig. 17. Detail of the spore base of a maturing specimen from Finland. The subtending hypha, still

persistent in this specimen, is somewhat recurved. The outer evanescent wall component is arrowed near the spore base.

F1821. Inner wall group (wall component 3), all from Finnish collections identified originally as G.fistulosum. Fig. 18. This specimen showsthe intrusion of the innermost wall component to give the erroneous impression of a septum (arrow). Fig. 19. Here, the innermost wall groupappears as an endospore after gentle crushing on a microscope slide. Fig. 20. In this specimen, the innermost wall group has separated as anendospore and collapsed after heavy crushing. The point of intrusion into the subtending hypha is arrowed. Fig. 21. At higher magnification

all wall components can be seen. Remnants of the evanescent component can be seen externally (bottom), and the septum sometimes formed bythe laminated component is evident (s, arrowed). The flexible component shows the intrusion into the subtending hypha (i, arrowed) at a higher

magnification than Fig. 20.

F2224. Germination of spores all from Finnish cultures originally identified as G.fistulosum. Fig. 22. Multiple germination tubes emergingdirectly through the spore wall (Gt, arrowed), stained in methyl blue. Fig. 23. A germ tube (Gt) emerging by regrowth from the subtending hypha,generally regarded as the normal method for species ofGlomus. Fig. 24. Greater detail of germ tubes (Gt) emerging directly through the spore

wall.

F2526. Roots, cleared and stained to reveal typical Glomusvesicular arbuscular mycorrhizas, with vesicles labelled (V). Fig. 25. Mycorrhizawith Paspalum notatum from the G. claroideum isotype collection. Fig. 27. Mycorrhiza with Plantago lanceolata from a Finnish pot culture

originally identified as G. fistulosum.

F2728. Evidence of contamination in type material ofGlomus claroideum. Fig. 27. Mycorrhiza on P.notatumwith a lobed vesicle, probablyofAcaulospora laeis. Fig. 28. A spore ofA.laeisshowing the scar (arrowed) at the point of spore formation typical of members of this genus.

microscopy, appears to form directly from the cytoplasmbounded by group 1. From our light-microscope obser-vations, we consider that it is not continuous with eithercomponent of group 1, but forms a distinct entity whichmight be termed an endospore.

In G. maculosum, the spores begin growth and appear toreach their ultimate size, with a simple, twolayered structuralwall, consisting of an evanescent component and a veryfinely laminated component. In an identical manner to G.

fistulosum and G. claroideum, as the spore develops, aflexible innermost component becomes evident. At maturity,this third component appears to be completely separatedfrom the subtending hypha and to form independently of it.Sometimes, there is a thin septum in the subtending hypha,near the spore base, but it is not consistently formed, and itis continuous with the innermost laminae of the laminatedwall component. The same type of structure (Fig. 21) can beseen in both G. fistulosumand G. claroideum.

The voucher collection of G. lamellosum (W1707) wasobtained directly from Canada as authenticated ex-typematerial. Spores have a wall structure of A(EL)B(F),

although because of fracturesor separations in the laminatedcomponent and loss of others, it could be interpreted asA(ELL)B(F) or A(LF) or even just A(L). The outermostwall on some specimens consists of two layers. This could beconsidered to be two different laminated components, but isprobably just a split lamina, since most spores have onlyone. The inner wall component seems to form an endospore-like structure, but is very difficult to detect on most


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T 3. Colours ofGlomus claroideum spores and of other species compared for similarity

Epithet Voucher Attemptculture Colour Observer

claroideum W2191 Field sample White (1) Walker Cclaroideum W538 Field sample (Hyalineone spore) to ochre to fulvous (Hyaline912). Walker Cclaroideum W1149 Field sample Hyaline to pale yellowish cream (Hyaline3) Walker C

claroideum W1404 576 Hyaline or white to pale ochraceous when older (Hyaline or 16). Walker C

claroideum W1467 577 Hyaline to white (Hyaline1) Walker Cclaroideum W2709 1052 Hyaline to pale yellowish cream. Walker C

claroideum W2499 1938 Pale yellowish cream to pinkish cream to yellowish cream (345) Walker Cclaroideum W2721 1939 White to ivory to pale yellowish cream (123) Broome A

claroideum W2839 2511 Hyaline to ivory when fresh. Ivory to pale ochraceous after 16 d in0025% sodium azide solution. (Hyaline2 or 26)

Walker C

claroideum W2847 2511 Ivory to pale yellowish cream to yellowish cream to pale ochraceous(2356)

Walker C

claroideum W388 4740 Pale ochraceous to ochraceous (68) Walker C

claroideum W2503 5975 White to pale yellow (no chart used) Walker Cclaroideum W2846 5976 (Ivory to) pale yellowish cream to yellowish cream to pale ochraceous-

ochraceous (to ochre) [(2)356 (8)]Walker C

claroideum W2056 5985 Ivory to pale yellowish cream to yellowish cream (234) Walker Cclaroideum W2845 5986 Pale yellowish cream (4) Walker Cclaroideum W2507 5986 Ivory to pale yellowish cream (23) Walker C

claroideum W947 6223 Hyaline to light yellow, becoming brown (after protologue, no chartused)

Schenck N

claroideum W2595 6223 Sienna to brick in these discoloured lactophenol-stored specimens.(1115)

Walker C

fistulosum W1498 54 Yellowish cream to pale ochraceous, a few pale apricot [56 (47)] Walker Cfistulosum W1779 56 Cream to yellowish cream to pale ochraceous (to ochraceous) [356

(8)]Walker C

fistulosum W1840 56 Ivory to yellowish cream to ochraceous (256) Walker Cfistulosum W1759 57 Cream to yellowish cream to pale ochraceous (356) Vestberg Mfistulosum W1841 58 Ivory to yellowish cream to pale ochraceous rarely ochraceous [256

(8)]Walker C

fistulosum W2371 59 Ivory to pale yellowish cream to yellowish cream to ochraceous toochre (235689)

Broome A

fistulosum W2427 510 Yellowish cream to ochraceous (58) Broome Afistulosum W2835 512 Ivory to yellowish cream (to pale ochraceous) [25 (6)] Walker Cfistulosum W2837 517 Ivory to pale yellowish cream to yellowish cream (235) Walker Cfistulosum W2844 519 Straw (50) after 9 d. Vestberg M

Straw to ochraceous (508) after 16 d

fistulosum W2374 431 Pale yellowish cream to pale ochraceous (36) Walker Cfistulosum W1853 743 Ivory to pale pinkish cream to yellowish cream (245) Vestberg M

fistulosum W1843 793 Ivory to pale yellowish cream (23) Vestberg Mfistulosum W2027 794 Ivory to pale ochraceous (26) Walker Cfistulosum W2269 796 Ivory to yellowish cream (25) Walker C

fistulosum W1520 2230 Pale ochraceous to buff a few spores apricot [652 (47)] Vestberg Mfistulosum W2871 2693 Dried sample ; ochraceous (8) Walker C

Fresh sample; ivory to pale yellowish cream (23)

fistulosum W1912 2715 Ivory to pale yellowish cream to yellowish cream to pale ochraceous(2356)

Walker C

fistulosum W2029 2715 Ivory to ochre but not pinkish cream (29 excluding 4) Walker Cfistulosum W1839 2717 Ivory to cream to pale ochraceous (236) Walker Cfistulosum W1947 27111 Yellowish cream to pale ochraceous to ochraceous to ochre (5689) Walker Cfistulosum W1972 3132 Very pale yellowish cream to yellowish cream (35) Vestberg M

fistulosum W2020 3132 Pale yellowish cream to yellowish cream (35) Vestberg Mfistulosum W2902 3134 Pale ochraceous to ochraceous (68) Walker C

fistulosum W1872 3353 Yellowish cream (5). No variation Walker Cfistulosum W2849 3833 Pale yellowish cream to yellowish cream to pale ochraceous to

ochraceous (3568)Vestberg M

fistulosum W2112 4201 Ivory (2) Vestberg Mfistulosum W2114 4221 Pale yellowish cream to pale pinkish cream (34) Vestberg Mfistulosum W2850 4353 Ivory to pale yellowish cream to yellowish cream (235) Vestberg Mfistulosum W2851 4803 Ivory to pale yellowish cream (23) Vestberg Mfistulosum W2370 5643 Ivory to pale yellowish cream to yellowish cream to pale ochraceous to

ochraceous (23568)Walker C


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T 3. (cont.)

Epithet Voucher Attemptculture Colour Observer

fistulosum W2840 6323 Ivory to pale yellowish cream (23) Vestberg Mfistulosum W2852 6343 Pale yellowish cream to pale pinkish cream to yellowish cream (345) Vestberg Mfistulosum W2853 6353 Ivory to pale yellowish cream to pale pinkish cream to yellowish cream

(2345)Vestberg M

maculosum W505 4910 Yellowish cream to pale ochraceous to ochraceous (568) afterformaldehyde

Miller D

maculosum W531 4911 Pale straw to ochraceous (508) Walker C

pustulatum W655 Field sample Sienna to cinnamon (1110) Walker Cpustulatum W1064 Field sample Pale yellow to yellow brown or orange brown Koske R

lamellosum W1707 2443 Pale ochraceous to ochraceous (68). Ivory when young (2) Walker Clamellosum W2117 2444 Yellowish cream to straw (550) Walker Clamellosum W2432 2444 White, yellowish cream to pale ochraceous (56) Broome Alamellosum W2712 2446 Hyaline to pale yellow Walker Clamellosum W2868 2446 Ivory to pale ochraceous (to ochre) [268 (9)] Walker Clamellosum W385 4720 Pale yellow Walker C

albidum W179 Field sample Dull white Walker Calbidum W79 2881 Hyaline to white (to off-white when mature) Walker Calbdium W169 2881 Hyaline to white (to off-white when mature) Walker Calbdium W170 2881 Hyaline to white (to off-white when mature) Walker Calbidum W258 2884 Dull white Walker C

albidum W282 4560 White Walker C

T 4. Spore dimensions (mean and ranges of length and widths in m) measured in a comparatie study ofGlomusclaroideumand similar fungi. Unless otherwise stated, measurements are from 100 spores in each sample

VoucherSpore length (m) Spore width (m)

Original identification Culture number Min Max Mean Min Max Mean

G. claroideum BR147 W2507 80 160 124 84 222 126G. claroideum BR147 W2845 95 181 128 95 178 128G. claroideum SC-09 W2417 72 192 129 75 192 129G. claroideum SC186 W2503 75 140 110 70 139 108G. claroideum SC186 W2846 65 154 108 70 165 109

G. claroideum Foul2 W2839 85 197 144 81 224 147G. claroideum Foul2 W2847 79 199 138 81 226 139G. claroideum Holotype W2595 63 181 129 51 188 130G. claroideum (n34) Isotype W947 95 175 130 92 205 133G. fistulosum G23a W1839 93 190 137 85 190 138G. fistulosum G23a W1842 87 169 122 87 175 124G. fistulosum Ex-type W1840 88 179 131 80 158 131G. fistulosum Ex-type W1841 80 197 135 80 243 135G. fistulosum Ex-type W2844 90 167 127 93 160 126G. fistulosum(n32) Ex-type W2837 99 201 137 111 160 136G. fistulosum V12 W2840 107 176 136 99 191 138G. fistulosum V13 W1872 83 165 124 93 179 125G. fistulosum V112a W2902 99 155 132 95 165 132G. fistulosum V127 W2114 99 176 136 99 183 138G. fistulosum V128 W1843 60 165 124 60 165 124G. fistulosum V138 W2020 84 153 124 80 160 126G. fistulosum(n121) V14b W1853 97 199 140 97 210 141

G. fistulosum V151 W2871 103 168 136 103 180 138G. fistulosum V170 W2849 88 153 123 84 153 123G. fistulosum(n122) V174 W2850 103 180 129 96 172 130G. fistulosum(n114) V184 W2851 68 168 125 79 168 126G. fistulosum V187 W2852 111 180 144 107 180 145G. fistulosum V198 W2853 92 164 124 92 168 126G. fistulosum V92 W2111 80 164 124 84 164 125G. fistulosum Irish. UCD1 W2370 94 181 124 92 165 125G. fistulosum Foul1 W2374 90 192 141 95 183 142G. lamellosum Ex-type W2868 84 219 136 81 174 135G. maculosum Isotype W505 102 178 138 102 178 139


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T5.Analysisoflengthsa

ndwidths(m)of100sporessampledfrompotculturesinthecomparatiestud

yofGlomusclaroideumandsimilarar

buscularmycorrhizal

fungi

Voucher

Width

rank

Length

rank

Tukey

Groupingfor

width

Mean

width

(m)

Tukey

Groupingfor

length

Mean

length

(m)

Attempt

number

Culture

number

Original

identification

Otheridentityandnotes

W2852

1

1

A

1453

A

1442

634

3

fistulosum

V187

W2839

2

2

B

A

1419

B

A

1419

251

1

claroideum

Foul2Sonch

us(JM)

W2374

3

3

B

A

1415

B

A

1410

43

1

claroideum

Foul2Raspberry(CW)

W1853

4

4

B

AC

1393

B

A

C

1386

74

3

fistulosum

V14b

W2847

5

5

B

AC

1388

B

A

C

1385

251

1

fistulosum

Foul1Sonch

us(JM)

W505

6

6

BDAC

1387

B

A

C

1381

491

0

maculosum

ISOTYPE

W1839

7

7

BDAC

1379

BDA

C

1368

271

7

fistulosum

Gryndler23A

W2871

8

9

BDAC

1379

EBDA

C

1359

269

3

fistulosum

V151

W2840

9

10

BDAC

1379

EBDA

C

1357

632

3

fistulosum

V12

W2114

10

8

BDAC

1378

EBD

C

1355

422

1

fistulosum

V127

W2868

11

12

BDEC

1352

EBDA

C

1360

244

6

lamellosum

Ex-type

W1841

12

11

BDEC

1348

EBDA

C

1357

5

8

fistulosum

Ex-type

W2902

13

13

FDEC

1320

ED

CF

1323

313

2

fistulosum

V112a

W1840

14

14

FDEC

1311

ED

GCF

1306

5

6

fistulosum

Ex-type

W2850

15

15

FDEC

1304

ED

G

F

1293

435

3

fistulosum

V174

W2595

16

16

FDE

1299

E

G

F

1291

622

3

claroideum

HOLOTYPE

W2845

17

17

F

E

1284

E

G

F

1280

598

6

claroideum

BR147A(INVAM)Dried

W2851

18

18

F

E

1283

E

G

F

1278

480

3

fistulosum

V184

W2844

19

19

F

E

1264

G

F

1266

5

19

fistulosum

Ex-type

W2507

20

24

F

E

1260

G

F

1239

598

6

claroideum

BR147A(INVAM)Fresh(UY)

W2112

21

22

F

E

1260

G

F

1243

420

1

fistulosum

V138

W2853

22

20

F

1256

G

F

1244

635

3

fistulosum

V198

W2111

23

23

F

1253

G

F

1240

223

3

fistulosum

V92

W1872

24

25

F

1250

G

1236

335

3

fistulosum

V13

W2370

25

21

F

1246

G

F

1244

564

3

fistulosum

Irish.

UCD1

W1843

26

26

F

1241

G

1235

79

3

fistulosum

V128

W1842

27

28

F

1241

G

1222

271

5

fistulosum

Gryndler23A

W2849

28

27

F

1233

G

1233

383

3

fistulosum

V170

W2846

39

30

G

1095

H

1079

597

6

claroideum

SC186(INVA

M)Fresh(UY)

W2503

30

29

G

1081

H

1097

597

5

claroideum

SC186(INVA

M)Dried


15/24


specimens and may be an artefact. The evanescent com-ponent is relatively thick (appearing unitary) on somespores, but has disappeared completely on others. Althoughit is assumed that this culture consists of just one species, itwas produced only from a multi-spore attempt, originally inopen pot culture. Consequently, there remains a possibilitythat more species were present in the pot, either from anoriginal error in selecting spores, or from later contami-nation. Two spores examined had pustules on the outerwall, reminiscent of those on G. pustulatum. The other ex-type material of this species came from three differentsubcultures of the ex-type. Each of these was started withpot culture substrate from its predecessor. The specimensfrom Attempt 2444 were from a sealed pot culture onPlantago lanceolata. In the first voucher, W2117, the wallstructure was observed on mature spores as A(EL)B(F).Some specimens had a luteous haloed effect due to the thickcoloured wall. Many of these spores were parasitized,apparently resulting in failure to develop the innermostflexible component. Specimens such as this appear to havea muronym of A(EL). Samples from the second voucher,

W2432 correspond with the illustrations in the protologue,but lack the flexible wall component. These spores areindistinguishable from those ofG.clarum. Later, the culturewas lost through a build up of parasites, but not before asample had been sent to Dr Dodd in Canterbury. Asubstrate sample from this culture from Kent (Attempt2445) was retrieved, and a voucher (W2392) taken beforethe remainder was used to establish Attempt 2446, insealed bags, with Plantago lanceolata. The W2392 collectionhas evanescent, laminated and flexible components typicalof the species examined here, though the flexible one is verythin and difficult to see, perhaps because the culture was notfully mature. Voucher W2712 from Attempt 2446 consistedonly of spores corresponding with the descriptions of G.

clarumand G. claroideum. A few spores possessed macularstructures yet showed no signs of attack by micro-organisms.The wall structure of the other sample from Attempt 2446,W2868, is A(JL)B(F) where J indicates a mucilaginous orjelly-like component. The J component is embedded withbacteria and fine particles and appears to be exuded by thefungus after the structural wall components have formed. Insome spores there is an additional structure that could beinterpreted as an evanescent component. Such spores havea muronym of A(JEL)B(F).

The spores of G. pustulatum have a wall structure ofA(UoL)B(F). The ornamentation (o) consists of roundedpustules or collicles on the outer wall surface. Although thewall structure description ofG. multisubstenum is given as

having only two inseparable layers, illustrations in theprotologue show evidence of both an outer, evanescentcomponent [remnants attached to the spore in Mukerji etal., 1983 their Figs 1, 2 and 4] and a flexible innercomponent [Mukerjiet al., 1983 their Fig. 4], correspondingto the wall-structure ofG.claroideum. The wall structure ofG.albidum, interpreted from the protologue, consists of anevanescent component surrounding a laminated component.However, re-examination of the type material and ofpreserved specimens from ex-type pot cultures showed thatit also may possess a very thin, flexible innermost wall

component. For the type specimens of G. przelewicense,there are two possible interpretations. Some spores have anevanescent component attached to a laminated component[A(EL)], whilst in a few specimens there could be anextremely thin flexible innermost component that can onlybe detected by wrinkling in the paler spores [A(ELF)]. Thereis no evanescent layer on the spores ofG.diaphanumwhichseems to have a wall structure of A(UF) or A(U)B(F), butwhich probably has a laminated outer component ratherthan a unitary one [A(LF) or A(L)B(F)].

Fistulae and pustules

Specimens from the type ofG.claroideumhave the sameoverall wall structure, and in one spore (Fig. 14) similarmaculae (Fig. 13) as G. maculosum. These occur on the innerwall component only, and like those ofG.maculosum, theyshow no clear evidence of invasion by parasitic micro-organisms. Re-examination of G. maculosum provided noevidence of an external agent that might have stimulated

formation of the maculae. On some spores, however, thereare unusual structures in the cytoplasm. Possibly these areinvasive parasites which have caused the fungus to react bylocalized deposition of wall material. Some spores in theculture of G. manihotis had developed maculae indis-tinguishable from those which were used to separate G.maculosumfrom other species in the genus. Evidence fromtwo other fungi examined during this study, one of G.claroideumand one of an undetermined Glomussp., showsthat these swellings are not confined to one species.

The ex-type material of G. lamellosum and the similarfungus found contaminating a culture ofG.mosseaeprovedto be confusing. Spores produced from these culturesdivided into three groups. One group had the characteristics

as described for the species, but another appeared to be G.claroideum and the third had the characteristics of G.clarum. In addition, spores similar to G. pustulatum werefound in one of the cultures of G. lamellosum. Glomus

pustulatumwas originally described from field collections. Ithas therefore not been proven that the production ofpustules on the surface of the spores is a consistent,genetically controlled character that can be used for speciesdelineation.

Although described from both field and pot-culturedspecimens, no samples ofG. multisubstensumremain in theherbarium at New Delhi, and none could be found (Tewari,Canada, pers. comm.; Mukerji, India, pers. comm.). It cantherefore be argued that the species was not validly

published. Nevertheless, it is illustrated sufficiently well inthe protologue to allow conclusions to be drawn about itsidentity, and we consider it worthwhile to make comparisonswith other species with similar descriptions, rather thanpursuing complex legalistic arguments.

We examined all 20 of the type specimens of G.przelewicense preserved in PVLG. These were fieldspecimens, and it was not easy to observe all the necessarycharacteristics. Nevertheless, with the exception possibilityofG. albidum, they did not fit well with any of the otherspecies. The difference between specimens ofG. diaphanum


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and the other species examined were distinctive, and theoriginal species description is substantially correct.

Reaction to PVLGMelzers

In the experimental evaluation, there was no reaction infresh spores ofG.fistulosumto PVLGMelezers, but in thedry spores a very weak pink reaction was noticed in-frequently. Although this may seem insignificant, it isrecorded for completeness. Apart from this, the reaction toMelzers reagent was tested in 31 different samples fromFinland, and except for one instance where a slight yellowingof laminae was recorded, there was no reaction. Similarly,there was only one occasion when a reaction to PVLGMelzers was noted (other than a slight yellowing of thelaminated wall component) in any other specimen amongall cultures examined. Specimens ofG.claroideum(W1404)displayed a rather slow, patchy orange reaction, probablyfrom the remnants of the evanescent wall component. Thereaction to Melzers reagent or PVLGMelzers of spores ofG. multisubstensum and G.przelewicense is unknown. Spores

of the species G. lamellosum are recorded in its protologueas reacting only by an increase in contrast of the laminationsin the main structural wall component. Neither of the G.diaphanum spore wall components has a reaction to Melzersreagent (from observations of W949, ex-type material),although it was not assessed for the isotype, W952.

Subtending hypha

The subtending hypha was usually more or less straight(Fig. 14) or slightly curved (Figs 15 and 23). On somespecimens, however, it was sharply recurved to the point offollowing the outline of the spore. In such specimens, it wasoften difficult to detect. Except for G. manihotis and G.

clarum, the subtending hyphae of all cultures examined inthis study develop in the same manner. In immature spores,it is two-layered and continuous with the layers of thesupporting mycelium. The point where the somatic hyphachanges into the spores subtending hypha is not alwayseasy to determine, but there is usually a gradual change incolour of the innermost component, where it becomespigmented and evidently laminated. As the spore matures,the outermost wall components usually beginto disintegrate.The evanescent wall and any gelatinous or mucigel-likestructures disappear, leaving only the rather thin laminatedcomponent which is normally short and rapidly tapering.Consequently, in such specimens, the subtending hypha isquite difficult or impossible to locate (Fig. 16). Spores ofG.

diaphanumand G. manihotisnormally retain a distinct andpersistent subtending hypha formed by a relatively muchlonger and sturdier laminated wall component. Due to thepoor condition of the type specimens ofG.claroideum, onlythe laminated component of the subtending hypha can beseen, though in some specimens it is split along the laminae,appearing then to consist of two components (Fig. 9).

Of all the G. claroideum-like species studied, 2 to 7% ofspores had at least two subtending hyphae. These wereusually fairly close together (Fig. 7), but on occasions theywere at opposite ends of the spore (Fig. 8).

Germination characteristics

Glomus fistulosum was the only species tested exper-imentally for germination characteristics. Results from thefrozen spores were 17, 39, 43, 50, 51 and 90% (six trials).For spores not given the freezing treatment, germinationwas 0, 6 and 61% (three trials only). Spores germinated intwo ways. Some produced regrowth directly through theremnants of the subtending hypha at thespore base (Fig. 23).This is considered to be the normal type of germinationfor Glomus spp. However, in other spores, up to five germtubes emerged from each spore by direct penetration of themain structural spore wall (Figs 22 and 24). Spores couldhave one or both of these germ tube emergence patterns. Afew spores in the ex-type and type material ofG.claroideumwere germinating at the time of preservation. Germinationis both through the subtending hypha and by direct growththrough the spore wall. The spores of G. maculosum arecapable of germinating by emergence of a germ tubethrough the subtending hypha (Miller and Walker 1986),but no experimental approach was taken in assessing

germination.There is no discussion of germination in the protologue ofG. lamellosum, but a few sporesof the G. clarum morphotypein the collection W2868 have germinated by direct regrowththrough the subtending hypha. No germination charac-teristics are recorded for G. pustulatum and nothing isknown of the germination characteristics of G. multi-substensum. The spores of G. albidum are described andillustrated in the protologue as germinating directly throughthe spore wall, but forG.przelewicenseno description of thegerminating characteristics is given in the original speciesdescription, and there are no germinating spores in the typematerial. The germination characteristics ofG. diaphanumare not described, and we have not been able to locate

germinating spores in specimens available to us.

Mycorrhizas

Glomus fistulosum forms mycorrhizas with abundantarbuscules and sparse, thin-walled vesicles (Fig. 26).However, Gryndler (pers. comm.) indicates that mycor-rhizas formed by the species (attempt 271) with Hedera helix(and occasionally in maize) are atypical, consisting mainlyof hyphal coils and atypical arbuscule-like structures formedby production of fine lateral hyphae branching directly fromthe coils. The same organism forms typical vesicular-arbuscular mycorrhizas with other hosts. The species also

produces spores in roots (Fig. 6), but these are sparse andnot always present in a sample.

Glomus claroideumis known to form vesicular arbuscularmycorrhizas, but no description is available other than thatthey are typical, and that spores were rarely produced inroots (Schenck and Smith, 1982). However, the holotypeincludes a microscope slide of stained mycorrhizas. Thesefall into two distinct categories (Figs 2527), a fairly typicalGlomus vesicular arbuscular mycorrhiza (Figs 25 and 26)(Abbott, 1982), and one with distinctly lobed vesicles (Fig.27). The cultures studied in the description ofG.maculosum


17/24


did not form typical arbuscular mycorrhizas. The mycor-rhizas that were formed were seen only to produce hyphalcoils, and neither vesicles nor arbuscules were noted.However, the fungus proved impossible to stain in the hostsused, and it is probable that arbuscules were present butwere not visualized.

According to the description in the protologue, G.lamellosum forms typical arbuscular mycorrhizas withvesicles, although Fig. 7 of that publication shows ratherstunted arbuscules. G. pustulatum is known to formarbuscular mycorrhizas with vesicles but there is nopublished detailed description, and although G. multi-substensum is said to form mycorrhizas, they are notillustrated. Glomus albidum forms vesicular arbuscularmycorrhizas but they are not illustrated in the description,whilst the mycorrhizal status ofG.przelewicense is unknown,the only known specimens consisting of spores collected inthe field. G. diaphanum forms both vesicular arbuscularmycorrhizas and abundant spores in roots.

D I S C U S S I O N

To avoid doubt, we must stress that our interpretation ofdevelopmental events is based on observations made bylight microscopy only, and the assumption (not necessarilytrue) that the spore wall structure advances from simple tocomplex. Our conclusions must inevitably, therefore, besubject to doubts that can probably only be solved byultrastructural observations. We believe that Stu rmer andMorton (1997) were in the same situation, and suggest thattheir phylogenetic and ontogenetic analysis must thereforebe subject to the same caveats, and may be premature andflawed. Stu rmer and Morton (1977) erroneously interpretearlier work (Walker, 1992), claiming that it suggests theinnermost layer in this group of organisms is evidence of

polyphyly. No such statement is made or implied in thatwork, which was written with the intention of pointing outunclear areas that were ripe for further research. Withregard to the flexible innermost wall, its ontogeny remainsunclarified, and until further studies are carried out,speculation about its analogies or homologies remains amatter of conjecture.

Doubt remains about the precise wall structure of thisspecies. Our interpretation of light microscopy observationsis that the inner wall of G. claroideum spores forms acomplete and separate entity developing only after thecompletion of the growth of the original spore. Therefore itmight not be correct to consider it to have the same kind ofblastosporic chlamydospore as is found in most other

species of the genus Glomus. Our interpretation is moreconsistent with an ectospore and endospore type ofdevelopment similar to that proposed for members of thegenus Scutellospora (Ferrer and Herrera, 1981). Stu rmerand Morton (1997) draw different conclusions, clearlystating, though not adequately illustrating, that the com-ponent is contiguous with the innermost lamina of the mainstructural wall component. Thus, there are two differentinterpretations possible from the same evidence. Theapparent endospore-like nature of the innermost wallcomponent may be an artefact of specimen preparation.

Ultrastructural developmental studies may be needed toascertain its true nature. We take a more cautious view thanStu rmer and Morton (1997) in proposing that there isevidence for an endospore, but accepting that the matterremains unresolved. We therefore sound a note of caution inwarning that any new phylogenetic analysis must be basedon sound, repeatable and unambiguous evidence.

The fact that germination can take place by directpenetration of multiple germination tubes through the sporewall is also different from the supposedly normal form ofgermination found in the genus Glomus (regrowth of thesubtending hypha). Such germination was discussed byWalker and Rhodes (1981), when the possibility of using itas a criterion for separating a new genus from Glomuswasdiscussed. The evidence is increasing, but more informationwill be required before a separation can be confidentlymade. Ideally, such studies would gather information frommany different sources. Suitable methods might includeultrastructural studies, DNA sequences of many differentgenes, isozyme profiles with several enzymes, and fatty acidprofiles.

Colour

Colour is a continuous variable that is rather difficult toassess, especially for the untrained observer. It is un-reasonable to expect to obtain a high degree of exactitude indefining and matching specimens with these characteristics,particularly when matched against charts made up byinexpensive printing processes. This is particularly true ofcolour charts made by the half-tone printing process(Gonnet, 1995). In this study, colour differences exist bothwithin and among isolates, but could only be used toseparateG.albidumandG.diaphanum. Spores of the formerare generally very much paler than those of most species

examined here, and the latter does not have pigmentedspores. Even these fall completely within a subset of the fullrange recorded for the other fungi which generally rangedfrom hyaline (only in very young, immature specimens)through ivory (2) and very pale creams (3 and 4) whenimmature, to a range of colours between yellowish cream (5)to ochraceous (8) for mature spores. More infrequently,older cultures have a small proportion of pale apricot (47)spores. Comparisons with colours quoted, from the half-tone chart used for G. claroideum (Stu rmer and Morton1997), show mostly the same range, depending on stage ofspore development, from white, through pale cream to darkcream which equates roughly to pale yellowish cream (3) topale ochraceous to ochraceous (368). The range of colours

we detected is broader than this, both paler and muchdarker, possibly as a result of different storage and culturingconditions, but we could find the full range in maturespecimens with their innermost wall component developed.Unfortunately, many species of the Glomales have spores inthis colour range, though few appear to have quite such abroad spectrum. Glomus multisubstensum spores are de-scribed as light brown, and the wall layers as brown orpale yellow brown in the species description, both ofwhich rather imprecise terms can be applied to mature andfield-collected specimens ofG.fistulosumandG.claroideum.


18/24


Spore colour varies considerably within and amongcultures, perhaps depending on such factors as age of theculture, soil conditions or host (Table 3). It is impossiblefrom the data we have to determine if these are due todifferences in perception among observers, differencescaused by age of culture, differences induced by physicalfactors such as pot culture substrate, or differences amongspores grown on different hosts. This variability can beviewed with some concern, since spore colour is oftenconsidered to be of considerable importance in speciesdescriptions among the members of the Glomales. Taxo-nomic characteristics must be consistent if they are to beused to separate organisms at any given taxonomic level.

Spore dimensions

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Synonymy Amongst the Arbuscular Mycorrhizal Fungi: Glomus claroideum, G. maculosum, G....

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