Evolution of Seed Plants: Gymnosperms & Angiosperms

1. Chapter 27 The Plant Kingdom: Seed Plants

2. Features of seeds • Primary means of reproduction and dispersal of • Gymnosperms • Angiosperms

3. Gymnosperm and angiosperm evolution

4. Features of seeds, cont. • Seeds are reproductively superior to spores • Embryonic development is further advanced • Seeds contain an abundant food supply • Each seed has a protective seed coat

5. The life cycle of a pine • A pine is a mature sporophyte • Pine gametophytes are small and nutritionally dependent on sporophyte • Pine is heterosporous and, in separate cones, produces • Microspores • Megaspores

6. The life cycle of a pine, cont. • Male cones produce microspores • Microspores develop into pollen grains • Pollen grains carried by air to female cones

7. Male and female cones in Pinus contorta

8. The life cycle of a pine, cont. • Female cones produce megaspores by meiosis • One megaspore develops into a female gametophyte in a megasporangium

9. The life cycle of a pine, cont. • After pollination, pollen tube penetrates megasporangium • Pollen tube reaches egg in the archegonium • After fertilization, zygote develops into embryo

10. Life cycle of pine

11. Features distinguishing gymnosperms from bryophytes and ferns • Vascular plants with seeds • Totally exposed or • On cones • Produce wind-borne pollen grains

12. The four phyla of gymnosperms • Phylum Pinophyta • Phylum Cycadophyta • Phylum Ginkgophyta • Phylum Gnetophyta

13. Conifers

14. Phylum Pinophyta • Conifers that produce • Wood • Bark • Needles • Seeds in cones • Most are monoecious

15. Phylum Cycadophyta • Look like palms or ferns • Dioecious, but reproduce with pollen and seeds in conelike structures • Once numerous, now few members left

16. Cycads A female coontie produces seed cones

17. Cycads This female cycad in South Africa has a trunk that reaches a height of about 9 m. Note immense seed cones, to 0.8 m long

18. Phylum Ginkgophyta • Sole member is Ginkgo biloba • Deciduous • Dioceious • Female ginkgo produces seeds directly on branches

19. Branch from a female ginkgo, showing exposed seeds and distinctive leaves

20. Gnetophytes • Consist of three genera • Gnetum • Ephedra • Welwitschia

21. Gnetophytes, cont. • Unique among gymnosperms, sharing traits with angiosperms • Vessel elements in their xylem • Cone clusters resemble flower clusters • Life cycle details resemble those of angiosperms

22. Leaves of Gnetum gnemon resemble those of flowering plants Male Ephedra has pollen cones clustered at the nodes

23. A specimen of Welwitschia mirabilis living in Namib Desert, Namibia – survives on fog

24. Angiosperms (phylum Magnoliophyta) • Vascular plants that produce flowers and seeds enclosed within a fruit • The most diverse and successful group of plants

25. Angiosperms (phylum Magnoliophyta), cont. • Flower may contain • Sepals • Petals • Stamens • Carpels

26. Angiosperms (phylum Magnoliophyta), cont. • Ovules are enclosed within an ovary • After fertilization • Ovules become seeds • Ovary develops into a fruit

27. Floral structure

28. Life cycle of an angiosperm • Sporophyte generation is dominant • Gametophytes are • Reduced in size • Nutritionally dependent on sporophyte generation

29. Life cycle of an angiosperm, cont. • Heterosporous • Within the flower, they produce • Microspores • Megaspores

30. Life cycle of an angiosperm, cont. • Microspore develops into a pollen grain • Megaspore develops into an embryo sac • Embryo sac contains seven cells with eight nuclei

31. Life cycle of an angiosperm, cont. • Egg cell and central cell with two polar nuclei participate in fertilization • Double fertilization resulting in formation of • Dipoid zygote • Triploid endosperm

32. Life cycle of flowering plants

33. Phylum Magnoliophyta is divided into two classes • Monocots • Dicots

34. Most monocots have • Floral parts in multiples of three • Seeds that each contain one cotyledon • Nutritive tissue in their mature seeds is endosperm

35. Simple pistil

36. Compound pistil

37. Most dicots have • Floral parts in multiples of four or five • Seeds that each contain two cotyledons • Nutritive organs in their mature seeds are the cotyledons

38. Evolutionary adaptations of flowering plants • Reproduce sexually by forming flowers • After double fertilization, seeds are formed within fruits

39. Evolutionary adaptations of flowering plants, cont. • Flowering plants have • Vessel elements in their xylem • Efficient carbohydrate-conducting sieve tube elements in their phloem • Wind, water, insects, or animals transfer pollen grains

40. Carpel of Drimys piperita

41. Evolution of gymnosperms • Seed plants arose from seedless vascular plants • Progymnosperms were seedless vascular plants • Megaphylls • “Modern” woody tissue

42. Evolution of gymnosperms, cont. • Progymnosperms probably gave rise to conifers • Progymnosperms probably gave rise to seed ferns, too • Seed ferns probably gave rise to cycads and ginkgo

43. Evolution of gymnosperms, cont. • Evolution of gnetophytes is unclear • Flowering plants probably descended from ancient gymnosperms

44. Fossil flower

45. Evolution of gymnosperms, cont. • Ancient gymnosperm have • Leaves with broad, expanded blades • Closed carpels

46. Evolution of gymnosperms, cont. • Flowering plants probably dicots • Amborella is a dicot that may be the nearest living relative to the ancestor of all flowering plants