Gymnosperms

Spring 2010

Outline

• Review of land plant phylogeny

• Characters of seed plants

• Gymnosperm phylogeny & diversity– Gnetophytes– Cycads– Gingko– Conifers

Review of land plant phylogeny

Green plants (viridophytes)

Land plants (embryophytes)

Vascular plants (tracheophytes)

Seed plants (spermatophytes)

Gymnosperms

Angiosperms

Figure 7.8 from the text

Figure 7.11 (Pt. 1) from the text

Figure 7.12 from the text

“Gymnosperms”Spermatophytes (Seed Plants)

and MORE!

Seed Ferns[FOSSIL]

seed: MANY CHARACTERS! – e.g., heterospory; reduction/retention of megaspore; integument/micropyle; nutritive tissue

vessel structure

axillary branching

vascular cambium [secondary xylem (wood) & secondary phloem) & cork cambium (cork)

male gametophyte: pollen grain & pollen tube

eustele

AngiospermsFlowering Plants

striate pollen

nonmotile sperm

double fertilization

nonmotile sperm

loss of lateral branches

Characters of seed plants

• Eustele• Axillary branching• Wood

– Cambia (vascular cambium, cork cambium)

• Seed– Heterospory– Megaspore reduction/retention– Integument/micropyle– Nutritive tissue

• Male gametophyte– Pollen grain– Pollen tube

eustele = primary stem vasculature comprising a single ring of vascular bundles

Characters of seed plants: Eustele

Characters of seed plants: axillary branching

cambia: vascular cambium (wood) & cork cambium (periderm)

Characters of seed plants: cambia

X-section of woody stem

Characters of seed plants: seed

• Heterospory

• Megaspore reduction/retention

• Integument/micropyle

• Nutritive tissue

MulticellularMulticellularSporophyteSporophyte

MulticellularMulticellularGametophyteGametophyte

Gametes[egg + sperm]

Zygote

MEIOSIS

Spores

2n

n

SYNGAMY<

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alternation of generations

[with sporangia]

[with gametangia: archegonia + antheridia]

Life cycle of most seed-free plants

embryocells in

sporangium

•homospory

MulticellularMulticellularSporophyteSporophyte

eggegg

Zygote

MEIOSIS

2n

n

SYNGAMY<

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alternation of generations

megasporangia

megasporangia

[archegoniaarchegonia]

embryo

Male GametophyteMale Gametophytespermsperm

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<Female GametophyteFemale Gametophyte

<microsporesmicrospores

megasporesmegaspores[antheridiaantheridia]

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microsporangia

microsporangia

Life cycle of seed plants•heterospory

Megaspore reduction:-reduction to 1 megaspore

Evolution of the seed

Megaspore retention:-the one megaspore is retained within megasporangium, not released

Evolution of the seed

Evolution of the seedEvolution of integument/micropyle fromsterile sporophyte tissue

•pollination droplet: -secreted by young ovule through micropyle -water + sugars, amino acids (megasporangium) -adhering pollen grains pulled inside!

Evolution of the seed

-nutritive tissue from the female gametophyte-integument becomes the seed coat

Evolution of the seed

Figure 7.11 (Pt. 2) from the text

male gametophyte•pollen grain = extremely reduced male gametophyte, a few cells•pollen tube – formed by the pollen, grows though sporophytic tissue to deliver sperm cells to egg (in ovule)

Characters of seed plants

Adaptive advantages of the seed:

Characters of seed plants: seed

•protection (seed coat)•dispersal unit of sexual reproduction•dormancy mechanisms•nutritive tissue – provides energy for young seedling, aiding in establishment

Two major groups of seed plants:

• Gymnosperms—not sure of the early evolutionary history of gymnosperms; could be monophyletic or could be paraphyletic

• Angiosperms—monophyly supported by many characters including the carpel

Gymnosperm Phylogeny

4 monophyletic lineages of gymnosperms

Gymnospermsmonophyletic

Gymnospermsparaphyletic

Gymnospermsparaphyletic

Gymnospermsmonophyletic

Figure 7.15 from the text

Gymnosperm diversity

-ca. 15 families, 75-80 genera, ca. 900 species-4 monophyletic lineages-all woody-mostly without effective vegetative reproduction-only tracheids in the xylem (except for gnetophytes, which also have vessels)-naked seeds-relatively slow sexual reproduction-worldwide but dominant in many colder or arctic regions-include the tallest, the most massive, and the longest living individual plants

Major groups of gymnosperms

• Gnetophytes

• Cycads

• Gingko

• Conifers

Gnetophyta—Gnetophytes or Gnetales 3 extant genera: Ephedra (65 spp.); Gnetum (28 spp.); Welwitschia mirabilis

related to angiosperms?•recent molecular data: a gymnosperm group

defined by many characters, e.g.:-opposite leaves, similar pollen-vessel structure (independent of angiosperms)-nonmotile sperm (independent?)-double fertilization (independent of angiosperms)-some with insect pollination

Major groups of gymnosperms

Gnetophyta - Gnetophytes

•Ephedra (65 spp.)-common desert shrub-reduced scale-like

leaves

Major groups of gymnosperms

Gnetophyta – Gnetales

•Gnetum (28 spp.)•tropical vines, trees, shrubs with opposite leaves that look like angiosperms!

Major groups of gymnosperms

Gnetales – Gnetophytes

•Welwitschia mirabilis-a strange plant native to deserts of Namibia,

sw Africa! -2 big curly leaves!

Major groups of gymnosperms

Cycadophyta – Cycads•squat, unbranched trunk (little wood), usually pinnately compound leaves•loss of axillary branching•dioecious: male and female plants•male and female strobili (cones)•motile, multiflagellate sperm! (ancestral)•coralloid roots with nitrogen-fixing cyanobacteria

Major groups of gymnosperms

Cycadophyta – Cycads

•ca. 11 genera (130 spp.)•now restricted distribution•seeds with bright fleshy seed coat--dispersed by plant-eating dinos!

Major groups of gymnosperms

A native U.S. cycad:Zamia floridana

Ginkgophytes – Ginkgo

extensive fossil record but…only1 living species: Ginkgo biloba!

•highly branched tree withwell developed wood

•deciduous, fan-shaped leaves with dichotomous venation•dioecious: male and female trees

-male: “cone” with lateral stalks bearing microsporangia-female: no cone, axis with 2 ovules

(outer integument layer fleshy)•motile sperm (ancestral)

Major groups of gymnosperms

Coniferophyta – Conifers•ca. 600 spp.•once dominant worldwide, displaced by angios•shrubs or small trees, highly branched with

well developed wood•leaves simple, often needle-like or awl-shaped

-pines: in fascicles•non-motile sperm (pollen tube needed)•female (seed-bearing) cones in most

Major groups of gymnosperms

Coniferophyta – Conifers

•pollen cone or male cone-microsporangia & modified leaves

•seed cone or female cone-axis with modified leaves (bracts, usually reduced), each subtending seed-bearing scale (modified branch system)-woody or leathery or fleshy

Major groups of gymnosperms

female

Coniferophyta – Conifers•seed cone and pine nuts

Major groups of gymnosperms

Korean pine nutsStone Pine nuts[w U.S.]

Conifers

Figure 8.23 from the text

Pinaceae

Leaves linear to needle-like

Ovules 2, invertedWinged seeds

Pollen usually with 2 appendages

Resin canals inwood & leaves

Abies (fir)

Pseudotsuga (Douglas fir)

Larix (larch)Picea (spruce)

Pinus(pines)

-needles in bundles-cone scales thickened atthe tip and often armed with a prickle

Cupressaceae

Leaves scale-like to linearPollen without appendages

Microsporangia 2-10 per microsporophyll &ovules 1-20 per cone scale

Cone scales fused to bracts

Juniperus (juniper)

Chamaecyparis

Taxodium (bald cypress)

Sequoia sempervirens (redwood) Sequoiadendron giganteum(giant sequoia)

Taxaceae

Seeds with a fleshy, brightly colored aril

Ovules solitary,cones lacking

Podocarpus

Araucariaceae