Gymnosperms

“The pine stays green in winter...wisdom in hardship.”

Western Mindanao State UniversityCollege of Science And Mathematics

Biology and Natural Sciences DepartmentBotLec 160- Plant Systematics

Introduction• Gymnosperm (DZHIM-no-sperm) is an informal term for all seed plants that have exposed

ovules so that pollen enters the micropyle. The term is derived from two Greek roots

that mean naked (“gymnos” -γσμνός) and seed (“sperma” -σπέρμα).

• The gymnosperms and angiosperms together compose the spermatophytes or seed

plants. By far the largest group of living gymnosperms is the

conifers (pines, cypresses, and relatives), followed by cycads, Gnetophytes

(Gnetum, Ephedra and Welwitschia), and Ginkgo (a single living species).

• The seed, one of the most marvellous products of evolution, is so complex that all seed

plants must be monophyletic, as evidenced by its vegetative tissues (e.g. stems) (Chaw et

al., 2000).

• Their naked condition stands in contrast to the seeds and ovules of flowering plants

(angiosperms), which are enclosed within an ovary.

• Gymnosperm seeds develop either on the surface of scales or leaves, often modified to

form cones, or at the end of short stalks as in Ginkgo.

• There are more than 1000 extant or currently living species of Gymnosperms in 88 plant

genera belonging to 14 plant families.

Characteristics

EVOLUTION

• Fossil record estimates indicate that gymnosperms must have evolved approximately 300 million

years ago from non-seed producing ancestors of the extinct division of Progymnospermophyta,

which were fern-like in appearance.

• Considering the relatively small number of living gymnosperms (about 720 species in 65 genera),

they are remarkably diverse in their reproductive structures and leaf types.

• not requiring water for sperm to swim in to reach the egg. Movement of pollen is air-borne.

Consequently, most gymnosperms produce huge amounts of pollen.

• Gymnosperms have major economic uses. Pine, fir, spruce, and cedar are all examples of conifers

that are used for lumber. Some other common uses for gymnosperms are soap, varnish, nail

polish, food, gum, and perfumes.

As land-dwelling plants developed further past ferns, several

modifications were developed for water conservation. These included:

• Gametophytes reduced; dependent on sporophyte. Sporophyte independent.

• Swimming sperm was replaced by dispersal of the whole male gametophyte

(pollen) by wind or insects. However, pollen contains sperm or at least

sperm nuclei.– Pollination—transfer of male gametophytes to the female plant. This still must be followed by

fertilization of the egg by a sperm nucleus which is produced by the male gametophyte.

• Seeds came into being.

• Two categories of seed-bearing plants are recognized:

the Gymnosperms (gymno = naked; sperma = seed), in which the seeds

develop on the surface of the reproductive structures (thus also called the

“naked-seed plants”) such as the cones in pine, and the Angiosperms (angio =

vessel, receptacle, container), in which seeds develop within a specialized

structure, called an ovary, on the adult sporophyte (also called the “flowering

plants”).

Representative Species

Origin and History

• Ideas about the ancestry of modern gymnosperms are suggested by the fossil record.

• PROGYMNOSPERMS (DIVISION Progymnospermophyta)

• Most likely the ancestors of the first plants that had seeds.

• Middle Devonian-Early Carboniferous period (ca. 360-310 mya)

• Treelike or shrub like resembling those of seed plants as well as the seedless vascular plants.

• DIVISION Pteridospermophyta

• Seed ferns.

• Late Devonian Period

• Became so abundant during the late Carboniferous period---Age of Ferns (Age of seed Ferns)

• Did not evolved from ferns! They are not just ferns with seeds! The seed ferns probably evolved

from the progymnosperms along an evolutionary line that has no modern descendants.

• DIVISION Cycadeoidophyta

• Superficial resemblance to Cycads

• Jurassic Period—Age of Cycads (Age of Dinosaurs)

• Extinct—end of Cretaceous Period (Dinosaurs extint) but Cycads still alive

• Differ from other gymnosperms (living or extinct) by having bisporangiate strobili—ovules and

microsporangia are on the same strobilus.

Phylogenetic Relationship

• Two of the most thorough studies of seed-plant phylogenies presented in cladogram:

• Peter Crane (Field Museum of Natural History, Chicago)

• James Doyle (University of California, Davis) and Michael Donoghue (Harvard University)

• Both used fossils as much as possible, although comparable characters of fossil and living plants

are often unknown because of the incompleteness of the fossil record.

Hypotheses differ in the selection

of the characters and the

significance placed on them for

inferring ancestor-descnedant

relationship.

Flowering plants are closest to

gnetophytes among extant

gymnosperms.

Division

Coniferophyta

Coniferophyta: Introduction

• Conifer– Latin ; conus (cone) and ferre (to bear), meaning the one that bears (a) cone(s).

• The conifers, Division Pinophyta, also known as

Division Ferophyta or Coniferae, are one of 13 or

14 division level taxa within the Kingdom Plantae.

• They are cone-bearing seed plants with vascular tissue;

• All extant conifers are woody plants, the great majority

being trees with just a few being shrubs.

• Typical examples of conifers include cedars, Douglas-

firs, cypresses, firs, junipers, kauri, larches, pines, hemlocks, re

dwoods, spruces, and yews.

• The division contains approximately 7 families, 68 genera, and

630 living species

Characteristics

• All living conifers are woody plants, and most are trees, the majority having monopodial growth

form (a single, straight trunk with side branches) with strong apical dominance.

• The size of mature conifers varies from less than one meter, to over 100 meters.

• The world's tallest, thickest, and oldest living trees are all conifers.

– The tallest is a Coast Redwood (Sequoia sempervirens), with a height of 115.55 meters

– The thickest, or tree with the greatest trunk diameter, is a Montezuma Cypress (Taxodium

mucronatum), 11.42 meters in diameter.

– The smallest is the pygmy pine (Lepidothamnus laxifolius) of New Zealand, which is seldom taller than

30cm tall when mature.

– The oldest is a Great Basin Bristlecone Pine (Pinus longaeva), 4,700 years old. Conflicting sources

claim that the largest tree by 3 dimensional volume is either: a Giant Sequoia (Sequoiadendrongiganteum), with a volume 1486.9 cubic meters or a Ficus Benghalensis named ThimmammaMarrimanu with volume unspecified.

• Many conifers have distinctly scented resin, secreted to protect the tree against insect infestation

and fungal infection of wounds. Fossilized resin hardens into amber.

• Primary vascular structure is a eustele. Vascular cambium allows secondary growth.

• Xylem is composed entirely of tracheids and wood is generally parenchyma poor and thus pycnoxylic

• As the name implies, the conifers are called “conifers” because they have cones. In this case, "cone" is a

colloquial term for a woody strobilus. As with other strobili we have studied, those of conifers are derived

from sporangia-bearing branch systems that have been modified.

• The sporophyte is heterosporous; the tiny gametophyte are nutritionally dependent upon the sporophyte.

• Most conifers are monoecious, all are wind-pollinated. Conifer seeds develop inside a protective cone called

a strobilus.

• The male cones have structures called microsporangia that produce yellowish pollen through meiosis.

Pollen is released and carried by the wind to female cones. Pollen grains produce pollen tubes, much like

those of angiosperms. When a pollen grain lands near a female gametophyte, it undergoes fertilization of the

female gametophyte.

• Alternatively, the gymnosperm male gametophytes are carried by wind to a female cone and are drawn into a

tiny opening on the ovule called the micropyle. It is within the ovule that germination occurs. From here, a

pollen tube seeks out the female gametophyte and if successful, fertilization occurs. In both cases, the

resulting zygote develops into an embryo, which along with its surrounding integument, becomes a seed.

Eventually the seed may fall to the ground and, if conditions permit, grows into a new plant.

• Many conifers are evergreen, that is they retain their leaves in winter.

• The leaves are needle-shaped. In the majority of conifers, the leaves are arranged spirally.

• Leaf size varies from 2 mm in many scale-leaved species, up to 400 mm long in the needles of some pines

(e.g. Apache Pine , Pinus engelmannii).

• five genera (Larix, Pseudolarix, Glyptostrobus, Metasequoia and Taxodium) are deciduous, shedding the

leaves in autumn and leafless through the winter.

• The seedlings of many conifers, including most of the Cupressaceae, and Pinus in Pinaceae, have a distinct

juvenile foliage period where the leaves are different, often markedly so, from the typical adult leaves.

• Do not form flowers or fruits

Seeds

• Consist of an embryo

• Stored food

• Seed coat

– Modern seed plant the ovule consist of a nucellusenvelope by one or two integuments with a micropyle(apical opening)

– When fertile the nucellus contains a megagametophytecomposed of nutritive tissue and archegonia

– After fertilization the integuments develop into a seed coat; a seed is formed

Characteristics of seed plants:

A. MegasporophyllsB. HeterosporyC. A reduced megagametophyte

retained within the megaspore D. A megaspore retained within a

fleshy megasporangium called a nucellus

E. Pollen - a structure which carries the male gamete to the female gamete

Seed plants do not require water for fertilization

Two Types of Cones

Staminate and Ovulate

Staminate Cones

The pollen-producing cones

Small, green, and inconspicuous near the tips of the branches

Shed after the pollen season is over

Ovulate ConesThe seed-producing cones

Larger than staminate cones

Size range: 1-2 inches

Woody structures consisting of layers of cone scales

Seeds develop between the cone scales

Seeds are generally winged

Evolution of an ovule

• Retention of the megaspores within the megasporangium(fleshy nucellus)- the megasporangium no longer releases the spores

• Reduction of megaspore mother cells to one functional megaspore in the megasporangium

• Formation of an endosporic(within the wall) megagametophyte that is no longer free-living- retained within the megasporangium

Evolution of an ovule

• Development of the embryo (young sporophyte) within the megagametophyteretained within the megasporangium

Evolution of an ovule

• Formation of an integument that completely envelops the megasporangiumexcept for the micropyle

• Modification of the apex of the megasporangium to receive microspores or pollen grains

Evolution of seeds

A. The seed habit arose by 365 million years ago via fusion of vegetative tissues around the megasporangium

1. This additional protective layer is called an integument

2. The integument has a small opening, the micropyle, through which fertilization takes place

3. Ovule = an integumentedmegasporangium

4. Following fertilization the integument will become the seed coat

Pine Tree Life Cycle

• Tree produces cones

• Pollen is carried by the wind from staminate cones to

ovulate cones

• Pollen lands on the open scales of the ovulate cone

• The scales then close tightly (in many pines the cone

begins to point downward

• Ovum is fertilized

• When the seeds are mature and environmental conditions

are right, scales open and release seeds

Representatives

For objectivity, the figure on the left shows the different FAMILIES

under Order Pinales of the Class Pinopsida, and Division

Pinophyta or Coniferophyta. Note that the Pinophyta was named due

to the abundancy of Pines among conifers. Taxonomically speaking,

the different families under Order Pinales are as follows:

Pinaceae

Araucariaceae

Podocarpaceae

Sciadopityaceae

Cupressaceae

Cephalotaxaceae

Taxaceae

From: http://en.wikipedia.org/wiki/Pinophyta

Pinaceae: The Pine family

• Resinous and evergreen trees or rarely shrubs growing

from 2 to 100 m tall, comprising about 9 genera and 225

species found mostly in temperate regions of the Northern

Hemisphere.

• The leaves are spirally disposed and are linear and

needlelike.

• The male or microsporangiate strobili are small, terminal, or

more often clustered along the stem axis, and consist of many

papery microsporophylls, each with two microsporangia on

the lower surface.

• The pollen grains typically have two, bladderlike wings.

• The female cones or megasporangiate strobili are woody and

often large, consisting of many ovuliferous scales, each with a

pair of adaxial ovules and a more or less distinct subtending

bract.

• Example species:– Abies pinsapo, Spanish fir.

– Cedrus atlantica, Atlantic cedar. This species has short lateral shoots with closelyspiralled leaves. Both male and female cones are terminal on these short spurs.

– Cedrus deodara, Note that 2 winged seeds separate from each ovuliferous scale.This genus is one of the exceptional ones for the family in that the conesdisintegrate while remaining on the tree. Nearly all of the scales have alreadyabscised from the axis of the cone.

Araucariaceae: The Aracauria Family

• The Araucariaceae are monoecious or dioecious trees

comprising two genera and about 30 species of the

Southern Hemisphere.

• The leaves are opposite or spirally arranged and are

needlelike to broad.

• The male or microsporangiate strobili are axillary or

terminal, comprising many spirally arranged

microsporophylls, each bearing 5-20 linear, pendant

microsporangia on the lower surface.

• The pollen grains lack wings. The female or

megasporangiate strobili are generally large and somewhat

woody, with numerous spirally disposed ovuliferous scales,

each fused with its bract and bearing a single median ovule

on the upper surface.

• Representative species:

– Araucaria araucana, monkey puzzle tree

– Araucaria columnaris, Cook pine.

Podocarpaceae: The Yellow-wood family

• large family of mainly Southern Hemisphere conifers, comprising

about 156 species of evergreen trees and shrubs. It contains

19 genera

• Native to Japan and Southern China, and commonly referred to as

Japanese Yew,

• Podocarpus is a tough, adaptable tree that is a very popular plant for

screens and hedges. Podocarpus has a dense growth habit.

• Its needle-like leaves are dark green above and paler beneath and

reach five inches in length and about one forth of an inch in width.

• Fertilized female cones produce attractive, edible, berry-like, purplish

fruits that ripen over the summer.

• Podocarpus is an evergreen, cold-hardy, drought-tolerant plant.

Showing best growth and form in full sun, Podocarpus will also grow

in shade but will grow more slowly and have a looser appearance. It

will tolerate a variety of well-drained, acidic soils; however, it does not

perform well on wet soils and may become yellow.

• Representative Species:

– Podocarpus macrophyllus. Note developing naked seed on fleshy "receptacle"

– Parasitaxus ustus. This monotypic genus from New Caledonia represents theworld's only known parasitic gymnosperm.

Sciadopityaceae: The Umbrella-pine family

• Sciadopitys verticillata, koyamaki, or Japanese umbrella-

pine, is a unique conifer endemic to Japan. It is the sole

member of the family Sciadopityaceae and genus

Sciadopitys, a living fossil with no close relatives, and

known in the fossil record for about 230 million years.

• Its genus name comes from the Greek prefix sciado-

meaning "shadow" and pitys, meaning "pine"; the specific

epithet means "with whorls".

• It is an evergreen tree that can grow 15-27m tall, with brown

main shoots bearing whorls of 7–12 cm long flexible green

cladodes that look like, and perform the function of

leaves but are actually composed of stem tissues;

occasionally, a cladode will be forked and produce a bud in

the 'v' of the fork. The cones are 6–11 cm long, mature in

about 18 months, and have flattish scales that open to

release the seeds.

• It is a very attractive tree and is popular in gardens, despite

its slow growth rate.

Cupressaceae: The Cypress family

• The Cupressaceae are monoecious or dioecious trees or

shrubs which include 27–30 genera (17 monotypic), whichinclude the junipers and redwoods, with about 130–140 speciesin total.

• The leaves are usually scale-like, and are opposite and

decussate, or whorled.

• The male or microsporangiate strobili are small and

inconspicuous, axillary or terminal, usually comprising only

a few microsporophylls, each with 3-6 or more

microsporangia. The pollen grains lack wings.

• The female or megasporangiate strobili are small, with 1-12

ovuliferous scales, each fused with its bract and bearing 2-

12 ovules. The scales may be flat and imbricate, peltate, or

connate. The female cone is woody or sometimes fleshy

and berrylike.

• Representative species:– Cupressus macrocarpa, Monterey cypress. A spreading crown like that seen

here is found in many species of this family. This species has female coneswith woody, peltate scales. Note the low number of scales per cone.

– Cupressus sempervirens var. stricta., Italian cypress.

– Juniperis sp., juniper.

Cephalotaxaceae: The Plum-yew family

• Small grouping of conifers, with three genera and about 20

species, closely allied to the Taxaceae

• These are much branched, small trees and shrubs.

• The leaves are evergreen, spirally arranged, often twisted at

the base to appear 2-ranked. They are linear to

lanceolate, and have pale green or white stomatal bands on

the undersides.

• The plants are monoecious, subdioecious or dioecious. The

male cones are 4-25 mm long, and shed pollen in the early

spring. The female cones are reduced, with one to a few

ovuliferous scales, and one seed on each ovuliferous scale.

• As the seed matures, the ovuliferous scale develops into

a fleshy aril fully enclosing the seed. The mature aril is

thin, green, purple or red, soft and resinous.

• Each ovuliferous scale remains discrete, so the cone

develops into a short stem with one to a few berry-like seeds.

They are probably eaten by birds or other animals which then

disperse the hard seed undamaged in their droppings, but

seed dispersal mechanisms in the family are not yet well

researched.

• Representative species:– Amentotaxus argotaenia

Amentotaxus assamica

– Cephalotaxus fortunei

Cephalotaxus griffithii

Toreya

Taxaceae: The Yew family

• Called the yew family, is a coniferous family which

includes seven genera and about 30 species of plants, or

in older interpretations three genera and 7 to 12 species.

• They are many-branched, small trees and shrubs.

• The leaves are evergreen, spirally arranged, often

twisted at the base to appear 2-ranked. They are linear to

lanceolate, and have pale green or white stomatal bands

on the undersides.

• The plants are dioecious, rarely monoecious. The

male cones are 2–5 millimetres (0.079–0.20 in) long, and

shed pollen in the early spring.

• The female cones are highly reduced, with just one

ovuliferous scale and one seed. As the seed matures, the

ovuliferous scale develops into a fleshy aril partly

enclosing the seed. The mature aril is brightly coloured,

soft, juicy and sweet, and is eaten by birds which then

disperse the hard seed undamaged in their droppings.

However, the seeds are highly poisonous to humans,

containing the poisons Taxine and Taxol

• Representative Species:– Torreya californica. In this species the seed is entirely enclosed in a fleshy aril.

In other members of the family the aril forms a fleshy cylinder that onlypartially envelops the otherwise naked seed.

Noteworthy Conifers: Douglas-fir

The Douglas-fir, named for David

Douglas, a 19th century Scottish

botanist. Great strength, stiffness

and moderate weight make it an

invaluable timber product said to be

stronger than concrete. Averaging up

to 200' in height and six feet in

diameter, heights of 325' and

diameters of 15' can also be found.

Provide more than ¼ of the timber cut in the U.S.

Noteworthy Conifers: Sequoia

In central California

Some are among the oldest

living things on earth (2,000

– 3,500 years)

273 feet tall

84 feet circumference

Bark 1 foot thick

Noteworthy Conifers: Bristlecone Pines

The oldest living bristlecones are found in

the White Mountains of California. The

oldest known living tree, discovered in

1957, is a 4,723-year-old patriarch

named Methuselah.

The oldest bristlecones are more than

4,000 years old. Egypt’s pyramids were

under construction when these trees

were seedlings!

Noteworthy Conifers: Coast Redwood

Redwood trees are the tallest living things on earth.

Some grow more than 350 feet tall.

CladisticsDIVISION CONIFEROPHYTA

PIN

AC

EAE

AR

AU

CA

CEA

E

PO

DO

CA

RPA

CEA

E

SCIA

DO

PIT

YAC

EAE

CU

PR

ESSA

CEA

E

CEP

HA

LOTA

XA

CEA

E

TAX

AC

EAE

GIN

KO

PH

YTA

Division Coniferophyta Cladogram