gymnosperms spring 2010. outline review of land plant phylogeny characters of seed plants gymnosperm...
TRANSCRIPT
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Gymnosperms
Spring 2010
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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
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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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“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
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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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eustele = primary stem vasculature comprising a single ring of vascular bundles
Characters of seed plants: Eustele
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Characters of seed plants: axillary branching
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cambia: vascular cambium (wood) & cork cambium (periderm)
Characters of seed plants: cambia
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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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MulticellularMulticellularSporophyteSporophyte
MulticellularMulticellularGametophyteGametophyte
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
embryocells in
sporangium
•homospory
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MulticellularMulticellularSporophyteSporophyte
eggegg
Zygote
MEIOSIS
2n
n
SYNGAMY<
<
<
<
<<
alternation of generations
megasporangia
megasporangia
[archegoniaarchegonia]
embryo
Male GametophyteMale Gametophytespermsperm
<
<Female GametophyteFemale Gametophyte
<microsporesmicrospores
megasporesmegaspores[antheridiaantheridia]
<
microsporangia
microsporangia
Life cycle of seed plants•heterospory
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Megaspore reduction:-reduction to 1 megaspore
Evolution of the seed
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Megaspore retention:-the one megaspore is retained within megasporangium, not released
Evolution of the seed
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Evolution of the seedEvolution of integument/micropyle fromsterile sporophyte tissue
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•pollination droplet: -secreted by young ovule through micropyle -water + sugars, amino acids (megasporangium) -adhering pollen grains pulled inside!
Evolution of the seed
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-nutritive tissue from the female gametophyte-integument becomes the seed coat
Evolution of the seed
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Figure 7.11 (Pt. 2) from the text
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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
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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
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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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Gymnospermsmonophyletic
Gymnospermsparaphyletic
Gymnospermsparaphyletic
Gymnospermsmonophyletic
Figure 7.15 from the text
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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
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Major groups of gymnosperms
• Gnetophytes
• Cycads
• Gingko
• Conifers
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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
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Gnetophyta - Gnetophytes
•Ephedra (65 spp.)-common desert shrub-reduced scale-like
leaves
Major groups of gymnosperms
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Gnetophyta – Gnetales
•Gnetum (28 spp.)•tropical vines, trees, shrubs with opposite leaves that look like angiosperms!
Major groups of gymnosperms
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Gnetales – Gnetophytes
•Welwitschia mirabilis-a strange plant native to deserts of Namibia,
sw Africa! -2 big curly leaves!
Major groups of gymnosperms
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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
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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
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A native U.S. cycad:Zamia floridana
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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
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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
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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
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Coniferophyta – Conifers•seed cone and pine nuts
Major groups of gymnosperms
Korean pine nutsStone Pine nuts[w U.S.]
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Conifers
Figure 8.23 from the text
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Pinaceae
Leaves linear to needle-like
Ovules 2, invertedWinged seeds
Pollen usually with 2 appendages
Resin canals inwood & leaves
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Abies (fir)
Pseudotsuga (Douglas fir)
Larix (larch)Picea (spruce)
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Pinus(pines)
-needles in bundles-cone scales thickened atthe tip and often armed with a prickle
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Cupressaceae
Leaves scale-like to linearPollen without appendages
Microsporangia 2-10 per microsporophyll &ovules 1-20 per cone scale
Cone scales fused to bracts
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Juniperus (juniper)
Chamaecyparis
Taxodium (bald cypress)
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Sequoia sempervirens (redwood) Sequoiadendron giganteum(giant sequoia)
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Taxaceae
Seeds with a fleshy, brightly colored aril
Ovules solitary,cones lacking
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Podocarpus
Araucariaceae