Gymnosperms Spring 2011

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 Evolution of wood before the evolution of seeds.

Figure 7.11 (Pt. 1) from the text

Figure 7.12 from the text

Spermatophytes (Seed Plants) “Gymnosperms” Angiosperms Flowering Plants nonmotile sperm loss of lateral branches and MORE! vessel structure striate pollen Seed Ferns [FOSSIL] double fertilization nonmotile sperm eustele axillary branching male gametophyte: pollen grain & pollen tube vascular cambium [secondary xylem (wood) & secondary phloem) & cork cambium (cork) seed: MANY CHARACTERS! – e.g., heterospory; reduction/retention of megaspore; integument/micropyle; nutritive tissue

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

Characters of seed plants: Eustele eustele = primary stem vasculature comprising a single ring of vascular bundles

Characters of seed plants: axillary branching

Characters of seed plants: cambia cambia: vascular cambium (wood) & cork cambium (periderm)

X-section of woody stem

Characters of seed plants: seed Heterospory Megaspore reduction/retention Integument/micropyle Nutritive tissue

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

Life cycle of seed plants heterospory Multicellular Sporophyte < embryo megasporangia Zygote < microsporangia < 2n < alternation of generations SYNGAMY MEIOSIS < n < microspores < sperm Male Gametophyte egg < [antheridia] megaspores < < Female Gametophyte [archegonia]

Evolution of the seed 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

Evolution of the seed 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

Figure 7.11 (Pt. 2) from the text

Characters of seed plants 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: seed Adaptive advantages of the 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

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

Gymnosperm diversity -ca. 15 families, 75-80 genera, ca. 1,000 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

Major groups of gymnosperms 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 Zamia Cycas

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!

A native U.S. cycad: Zamia floridana

Major groups of gymnosperms 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 Pinus female

Major groups of gymnosperms Coniferophyta – Conifers seed cone and pine nuts Stone Pine nuts [w U.S.] Korean pine nuts

Figure 8.23 from the text Pinaceae, Taxaceae, Cupressaceae Conifers

Pinaceae Pinus Pollen usually with 2 appendages Picea Leaves linear to needle-like Pinus Resin canals in wood & leaves Pinaceae Pinus Pinus Winged seeds Ovules 2, inverted

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

Pinus (pines) -needles in bundles -cone scales thickened at the tip and often armed with a prickle

Cupressaceae Pollen without appendages Leaves scale-like to linear Juniperus Chamaecyparis Pollen without appendages Leaves scale-like to linear Cryptomeria Juniperus Cone scales fused to bracts Microsporangia 2-10 per microsporophyll & ovules 1-20 per cone scale Cupressaceae

Juniperus (juniper) Taxodium (bald cypress) Chamaecyparis

Sequoiadendron giganteum Sequoia sempervirens (redwood) Sequoiadendron giganteum (giant sequoia)

Taxaceae Taxus Ovules solitary, cones lacking Seeds with a fleshy, brightly colored aril

Podocarpus Araucariaceae (Araucaria)