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Gymnosperms Spring 2011
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Outline Review of land plant phylogeny Characters of seed plants
Gymnosperm phylogeny & diversity Gnetophytes Cycads Gingko Conifers
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Review of land plant phylogeny
Green plants (viridophytes) Land plants (embryophytes) Vascular plants (tracheophytes) Seed plants (spermatophytes) Gymnosperms Angiosperms
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Figure 7.8 from the text Evolution of wood before the evolution of seeds.
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Figure 7.11 (Pt. 1) from the text
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Figure 7.12 from the text
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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
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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
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Characters of seed plants: Eustele
eustele = primary stem vasculature comprising a single ring of vascular bundles
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Characters of seed plants: axillary branching
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Characters of seed plants: cambia
cambia: vascular cambium (wood) & cork cambium (periderm)
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X-section of woody stem
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Characters of seed plants: seed
Heterospory Megaspore reduction/retention Integument/micropyle Nutritive tissue
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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]
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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]
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Evolution of the seed Megaspore reduction: -reduction to 1 megaspore
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Evolution of the seed Megaspore retention:
-the one megaspore is retained within megasporangium, not released
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Evolution of the seed Evolution of integument/micropyle from
sterile sporophyte tissue
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Evolution of the seed pollination droplet:
-secreted by young ovule through micropyle -water + sugars, amino acids (megasporangium) -adhering pollen grains pulled inside!
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Evolution of the seed -nutritive tissue from the female gametophyte
-integument becomes the seed coat
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Figure 7.11 (Pt. 2) from the text
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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)
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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
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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
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Gymnosperm Phylogeny 4 monophyletic lineages of gymnosperms
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Figure 7.15 from the text Gymnosperms paraphyletic Gymnosperms monophyletic Gymnosperms monophyletic Gymnosperms paraphyletic
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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
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Major groups of gymnosperms
Gnetophytes Cycads Gingko Conifers
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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
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Major groups of gymnosperms
Gnetophyta - Gnetophytes Ephedra (65 spp.) -common desert shrub -reduced scale-like leaves
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Major groups of gymnosperms
Gnetophyta – Gnetales Gnetum (28 spp.) tropical vines, trees, shrubs with opposite leaves that look like angiosperms!
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Major groups of gymnosperms
Gnetales – Gnetophytes Welwitschia mirabilis -a strange plant native to deserts of Namibia, sw Africa! -2 big curly leaves!
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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
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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!
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A native U.S. cycad: Zamia floridana
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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)
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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
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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
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Major groups of gymnosperms
Coniferophyta – Conifers seed cone and pine nuts Stone Pine nuts [w U.S.] Korean pine nuts
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Figure 8.23 from the text Pinaceae, Taxaceae, Cupressaceae Conifers
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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
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Pseudotsuga (Douglas fir)
Abies (fir) Picea (spruce) Larix (larch)
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Pinus (pines) -needles in bundles -cone scales thickened at
the tip and often armed with a prickle
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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
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Juniperus (juniper) Taxodium (bald cypress) Chamaecyparis
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Sequoiadendron giganteum
Sequoia sempervirens (redwood) Sequoiadendron giganteum (giant sequoia)
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Taxaceae Taxus Ovules solitary, cones lacking
Seeds with a fleshy, brightly colored aril
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Podocarpus Araucariaceae (Araucaria)
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