1. Life on Earth Kingdom Plantae Part IV
The Seed Plants: Gymnosperms

3. Origin of the Seed Female Gametophyte Scenario
Megasporangium produces only one functional megaspore
Megaspores are not released from the plant
Megaspore develops into the female gametophyte within the old megasporangium

4. Origin of the Seed (cont.)
Archegonia are formed with egg cells and fertilized in situ
Embryo (new sporophyte) develops surrounded by female gametophyte tissue and old megasporangium wall (nucellus)

5. Origin of the Seed (cont.)
Megasporophyll surrounds the structure and acts as integument (seed coat)
The mature ovule (seed) is released from the plant (old sporophyte)

6. Origin of Pollen Male Gametophyte Scenario
Micorsporophylls produce microsporangia
Microspores (N) are not released from the microsporangium but divide to form a 4-celled microgametophyte (pollen grain)
Four cells are 2 prothallial cells, 1 generative cell and 1 tube cell

7. Pine Pollen

8. Origin of Pollen (cont.)
Pollen grains (male gametophytes) are released from the “strobilus” or “cone”
The pollen grains germinate forming a pollen tube
The generative cell divides to form sperm nuclei which travel down the pollen tube to fertilize the egg

9. Why evolve seeds and pollen?
Embryo is well protected in the seed coat
Seeds can be “dormant” and wait for suitable growth conditions
Transfer of pollen (male to female) does not require water like sperm

10. Why evolve seeds and pollen? (cont.)
Embryo has a ready supply of nutrients for early development (female gametophyte tissue)
A seed is an excellent dispersal unit (wind, animals)

11. Seed Plant Divisions Gymnosperms Angiosperms
plants with “naked” seeds not found in a fruit
includes 4 Divisions
Angiosperms
seed plants with “hidden” seeds, i.e. formed inside a fruit
only one Division

12. Gymnosperms
Coniferophyta
Cycadophyta
Ginkgophyta
Gnetophyta

13. Division Coniferophyta
Most species are monoecious, woody perennials producing cones
Some are deciduous, most are evergreen with needle-like leaves
Extended life cycle (3 years)

14. Primary vs. Secondary Growth
Primary tissues are derived from meristems
Zones of cell division in root tips, shoot tips, axillary buds etc.
Primary growth generally creates elongation of stems, branches, and roots or creates reproductive organs

15. Primary vs. Secondary Growth (cont.)
Secondary tissues are derived from cambia
Cambial activity generally causes increase in girth of the plant (root, stem)
Woody plants develop 2 cambia:
vascular cambium (producing secondary xylem and phloem)
cork cambium (producing “bark” layers)

16. Pine Anatomy (stem) PITH RESIN DUCT VASCULAR CAMBIUM SECONDARY XYLEM
SECONDARYPHLOEM

17. RADIAL
Wood Sections
TRANSVERSE
Wood Rays
TANGENTIAL

18. Pine Needles

19. Pine Life Cycle
Trees produce both male (staminate) and female (ovulate) cones
Male cones are usually lower on the tree to assist with out-crossing
Pollination takes place in the spring when female cones are small (about 1/2 inch)

20. Pine Life Cycle (cont.)
Development of the mature ovule with archegonia takes more than a year
Pollen tube digests its way slowly through the nucellus to the archegonium for fertilization
Nearly another year is required before the embryo is mature and the female cone opens to release the seeds

21. Pine Life Cycle

22. Pinus (male and female cones)

23. Male Cone (longitudinal Section)

24. Conifer Diversity
Highly diverse in both Northern and Southern Hemispheres
Includes pine, spruce, hemlock, fir, Douglas fir, yew, juniper, cypress, sequoia, larch, podocarps, araucarias and others

25. Taxodium (bald cypress)

26. Taxus (yew) with female cones
Giant Sequoia
Taxus (yew) with female cones

27. Sequoia and Sequoiadendron

28. Araucaria family –Wollemi “pine,” discovered living in Australia, 1994, known from Jurassic fossils

29. Aucariaceae (Southern Hemisphere)
Norfolk Island Pine

30. Division Cycadophyta
Perennial, dioecious plants with coarse palm-like leaves
Female cones are often very large
Only 10 genera known - many with highly restricted ranges, primarily tropical
Produce flagellated sperm

31. Cycas revoluta and C. media
With “female cone” and seeds

32. Dioon edule

33. Encephalartos

34. Division Ginkgophyta Ginkgo biloba only species
Probably extinct in the wild (originally from China)
Separate male and female trees (dioecious)

35. Division Ginkgophyta (cont.)
Female ovules produce butyric acid (plant males!)
Male trees produce small, fleshy pollen cones; motile sperm are produced
Tolerates air pollution well

36. Ginkgo biloba

37. Ginkgo Leaves and Ripe Ovules

38. Division Gnetophyta
Gnetum, Ephedra (Mormon Tea) and Welwitschia very different organisms
Have vessels in the xylem
Do not produce multicellular archegonia
Have double fertilization
Ephedra male cones

39. Gnetophyta (cont.)
Gnetum is a genus of tropical vines with flowering plant-like leaves
Ephedra is a desert shrub with several species in the SW United States (called Mormon Tea)
Welwitschia mirabilis is a bizarre, tap-rooted, perennial plant of the desert areas of SW Africa

40. Ephedra nevadensis

41. Welwitschia mirabilis
Habitat view in SW Africa

42. Welwitschia mirabilis in Namib Desert, Namibia

43. Welwitschia mirabilis -female (with ovulate cones)

44. Welwitschia mirabilis - male (with staminate cones)

45. Gnetum
With Ovules

46. Importance of Gymnosperms
Major source of lumber for construction
Primary source of pulp for paper manufacture
Many ornamentals
Source of resins for turpentine, rosin (“naval stores”)
Juniper (“berries”) used to flavor gin
Source of amber and even lemon flavoring
Anticancer drug taxol from Pacific yew bark/ English yew leaves

47. Importance of Gymnosperms
Originally took 4 trees to produce a single human dose!
Now, using leaves of common English yew, a synthetic process makes the drug.
TAXOL:
31 years from “bark” to “business”