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 Angiosperms Flowering 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

MulticellularSporophyte MulticellularGametophyte Gametes [egg + sperm] Zygote MEIOSIS Spores 2n n SYNGAMY < < < < < < < < alternation of generations [with sporangia] [with gametangia: archegonia + antheridia] Life cycle of most seed-free plants embryo cells in sporangium homospory

MulticellularSporophyte egg Zygote MEIOSIS 2n n SYNGAMY < < < < < < alternation of generations megasporangia archegonia [archegonia] embryo Male Gametophyte sperm < < Female Gametophyte < microspores megaspores antheridia [antheridia] < 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 integument/micropyle from sterile 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

Gymnosperms monophyletic Gymnosperms paraphyletic Gymnosperms paraphyletic Gymnosperms monophyletic Figure 7.15 from the text

Gymnosperm diversity -ca. 15 families, 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…only 1 living species: Ginkgo biloba! highly branched tree with well 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, inverted Winged seeds Pollen usually with 2 appendages Resin canals in wood & leaves

Abies (fir) Pseudotsuga (Douglas fir) Larix (larch)Picea (spruce)

Pinus (pines) -needles in bundles -cone scales thickened at the 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