seed plants & gymnosperms spring 2014. outline review of land plant phylogeny characters of seed...
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Seed Plants & Gymnosperms
Spring 2014
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Outline
• Review of land plant phylogeny• Characters of seed plants• Gymnosperm phylogeny & diversity
– Cycads– Gingko– Conifers– Gnetophytes
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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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Evolution ofwood before the evolutionof seeds.
Fig. 5.1
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Seed fern(wood, seeds)
Progymnosperm(wood, no seeds)
Fossil lignophytes
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Seed fern fossils from Pella, Iowa
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Evolution ofwood (>380 mya) before the evolutionof seeds (>360 mya).
Fig. 5.1
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Characters of seed plants
• Eustele (ancestral)• Axillary branching• Wood (ancestral)
– 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
Leaf traces
Bud/branch traces
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cambia: vascular cambium (wood) & cork cambium (periderm)
Characters of seed plants: cambia
Fig. 5.3
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X-section of woody stemFig. 5.4
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Characters of seed plants: seed
• Heterospory
• Megaspore reduction/retention
• Integument/micropyle
• Nutritive tissue
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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
embryocells in
sporangium
• homospory
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MulticellularSporophyte
egg
Zygote
MEIOSIS
2n
n
SYNGAMY<
<
<
<
<<
alternation of generations
megasporangia
[archegonia]
embryo
Male Gametophytesperm
<
<Female Gametophyte
<microspores
megaspores[antheridia]
<
microsporangia
Life cycle of seed plants• heterospory
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Megaspore reduction:-reduction to 1 megaspore
Evolution of the seed
reduction to 1 megasporeFig. 5.6 #3
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Megaspore retention:-the one megaspore is retained within megasporangium, not released
Evolution of the seed
Fig. 5.6 #4
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Evolution of the seedEvolution of integument/micropyle fromsterile sporophyte tissue
Fig. 5.6 #5
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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
Fig. 5.10
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-nutritive tissue from the female gametophyte-integument becomes the seed coat
Evolution of the seed
Fig. 5.10
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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
Pine pollen
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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
Cycads Gingko Pines Gnetales Cypresses et al.
1° DNA data
pollen tube
simple leaves
compound ♀cones (strobili)
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Gymnosperm diversity
-ca. 15 families, 75-80 genera, ca. 1,000 species-4 or 5 main 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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Gymnosperm wood: tracheids only
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Major groups of gymnosperms
• Cycads
• Gingko
• Conifers
• Gnetophytes
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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
Zamia female strobilus
Cycas male strobilus
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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Gymnosperm Phylogeny
Cycads Gingko Pines Gnetales Cypresses et al.
1° DNA data
pollen tube
simple leaves
compound ♀cones (strobili)
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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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Ginkgophytes – Ginkgo
Major groups of gymnosperms
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Fig. 5.1
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Coniferophyta – Conifers• ca. 700 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• include both traditional conifers but now
also the Gnetales (gnetophytes)
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
male
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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Fig. 5.19
Evolution of the compound conifer female cone
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Gymnosperm Phylogeny
Cycads Gingko Pines Gnetales Cypresses et al.
1° DNA data
pollen tube
simple leaves
compound ♀cones (strobili)
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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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Gymnosperm Phylogeny
Cycads Gingko Pines Gnetales Cypresses et al.
1° DNA data
pollen tube
simple leaves
compound ♀cones (strobili)
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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
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Gymnosperm Phylogeny
Cycads Gingko Pines Gnetales Cypresses et al.
1° DNA data
pollen tube
simple leaves
compound ♀cones (strobili)
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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