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Gymnosperms

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)

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Gymnosperms

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  1. Gymnosperms Spring 2011

  2. Outline • Review of land plant phylogeny • Characters of seed plants • Gymnosperm phylogeny & diversity • Gnetophytes • Cycads • Gingko • Conifers

  3. Review of land plant phylogeny Green plants (viridophytes) Land plants (embryophytes) Vascular plants (tracheophytes) Seed plants (spermatophytes) Gymnosperms Angiosperms

  4. Figure 7.8 from the text Evolution of wood before the evolution of seeds.

  5. Figure 7.11 (Pt. 1) from the text

  6. Figure 7.12 from the text

  7. 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

  8. 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

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

  10. Characters of seed plants: axillary branching

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

  12. X-section of woody stem

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

  14. 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]

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

  16. Evolution of the seed • Megaspore reduction: • -reduction to 1 megaspore

  17. Evolution of the seed • Megaspore retention: • -the one megaspore is retained within • megasporangium, not released

  18. Evolution of the seed Evolution of integument/micropyle from sterile sporophyte tissue

  19. Evolution of the seed • pollination droplet: • -secreted by young ovule through micropyle • -water + sugars, amino acids (megasporangium) • -adhering pollen grains pulled inside!

  20. Evolution of the seed -nutritive tissue from the female gametophyte -integument becomes the seed coat

  21. Figure 7.11 (Pt. 2) from the text

  22. 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)

  23. 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

  24. 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

  25. Gymnosperm Phylogeny 4 monophyletic lineages of gymnosperms

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

  27. 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

  28. Major groups of gymnosperms • Gnetophytes • Cycads • Gingko • Conifers

  29. 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

  30. Major groups of gymnosperms • Gnetophyta - Gnetophytes • Ephedra (65 spp.) • -common desert shrub • -reduced • scale-like • leaves

  31. Major groups of gymnosperms • Gnetophyta – Gnetales • Gnetum (28 spp.) • tropical vines, trees, shrubs with opposite leaves that look like angiosperms!

  32. Major groups of gymnosperms • Gnetales – Gnetophytes • Welwitschia mirabilis • -a strange plant native to deserts of Namibia, • sw Africa! • -2 big curly leaves!

  33. 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

  34. 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!

  35. A native U.S. cycad: Zamia floridana

  36. 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)

  37. 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

  38. 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

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

  40. Figure 8.23 from the text Pinaceae, Taxaceae, Cupressaceae Conifers

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

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

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

  44. 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

  45. Juniperus (juniper) Taxodium (bald cypress) Chamaecyparis

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

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

  48. Podocarpus Araucariaceae (Araucaria)

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