1. 29 The Evolution of Seed Plants

2. 29 The Evolution of Seed Plants 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? 29.2 What Are the Major Groups of Gymnosperms? 29.3 What Features Distinguish the Angiosperms? 29.4 How Did the Angiosperms Originate and Diversify? 29.5 How Do Plants Support Our World?

3. Ch.29 Land plants retain derived features they share with green algae: Chlorophyll a and b. Starch as a storage product. Cellulose in cell walls

4. Ch.29 The vascular system consists of tissue specialized for the transport of materials. Xylem conducts water and minerals from soil up to aerial parts of plant. Some cells have lignin—provides support. Phloem conducts products of photosynthesis through plant

5. Ch.29

6. Figure 29.1 Highlights in the History of Seed Plants

7. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Surviving seed plants fall into two groups: Gymnosperms “naked seed”: pines and cycads Angiosperms “enclosed seed”: flowering plants

8. Figure 29.2 The Major Groups of Living Seed Plants

9. Ch.29 Plants have a life cycle that alternates between a Gametophyte (n) stage- produces gametes Sporophyte (2n)stage- produces spores This is called alternation of generations.

10. Ch.29

11. Plant Life Cycles

12. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Gametophyte generation is reduced. Haploid gametophyte develops partly or entirely while attached to the sporophyte.

13. Figure 29.3 The Relationship between Sporophyte and Gametophyte Has Evolved (Part 1)

14. Figure 29.3 The Relationship between Sporophyte and Gametophyte Has Evolved (Part 2)

15. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Only earliest gymnosperms had swimming sperm. Without swimming sperm, seed plants were able to be independent of water for sexual reproduction; an advantage for existence on land.

16. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Seed plants are heterosporous: produce two types of spores. One becomes female gametophyte, one becomes male gametophyte. Seed plants form separate megasporangia and microsporangia.

17. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Spores are produced in sporangia by meiosis. Megaspores develop into female gametophytes within the megasporangia. Only one meiotic product survives and develops into the megagametophyte by mitotic divisions.

18. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Megagametophyte (haploid) produces an egg by mitosis. Megagametophyte houses the next sporophyte generation when egg is fertilized.

19. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Megasporangium is surrounded by integument made of sporophytic structures. Megasporangium and the integument together form the ovule, which develops into a seed.

20. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? In the microsporangium, microspores divide mitotically to produce the male gametophyte, or pollen grain.

21. Figure 29.4 Pollen Grains

22. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Pollination: when a pollen grain lands near a female gametophyte. A pollen tube is produced that digests its way through the sporophyte tissue to the megagametophyte. Sperm are released from the tube, and fertilization results in a diploid zygote.

23. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Diploid zygote divides to produce an embryonic sporophyte. Growth is then suspended, the embryo enters a dormant stage, with the end product being a multicellular seed.

24. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Seeds have tissues from three generations: Seed coat develops from the sporophyte parent (integument). Female gametophytic tissue from the next generation contains a nutrient supply for developing embryo. Embryo is the new sporophyte generation.

25. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Seeds are well-protected resting stages. May remain viable for many years, germinating when conditions are favorable. Seed coat protects from drying out as well as predators. Many seeds have adaptations for dispersal.

26. 29.1 How Did Seed Plants Become Today’s Dominant Vegetation? Seeds are one of the main reasons for the success of seed plants—the dominant life forms in terrestrial environments. Secondary growth also contributes to their success. Wood: proliferated xylem, gives support and allows plants to grow above their competitors for sunlight.

27. 29.3 What Features Distinguish the Angiosperms? Female gametophyte even more reduced— usually only seven cells. Trend throughout evolution of vascular plants: sporophyte generation becomes larger, gametophyte generation becomes smaller, and more dependent on sporophyte.

28. 29.3 What Features Distinguish the Angiosperms? Synapomorphies (shared traits) in angiosperms: Double fertilization Triploid endosperm Ovules and seeds enclosed in a carpel Flowers Fruits Xylem with vessel elements and fibers Phloem with companion cells

29. 29.3 What Features Distinguish the Angiosperms? Double fertilization: Microgametophyte has two male gametes. Nucleus of one combines with egg. The other nucleus combines with two haploid nuclei of female gametophyte to form a triploid nucleus—becomes the endosperm. Endosperm nourishes developing sporophyte.

30. 29.3 What Features Distinguish the Angiosperms? Angiosperm: “enclosed seed”—the ovules and seeds are enclosed in a modified leaf called a carpel. Carpels provide protection, and may interact with pollen to prevent self- pollination.

31. 29.3 What Features Distinguish the Angiosperms? Flowers: Stamens bear microsporangia: consist of filament and anther. Carpels bear megasporangia. One or more carpels form the pistil—stigma, style, and ovary.

32. Figure 29.9 A Generalized Flower

33. 29.3 What Features Distinguish the Angiosperms? Petals (corolla) and sepals (calyx) are modified leaves. Often play a role in attracting pollinators. The calyx often protects the flower bud before it opens.

34. 29.3 What Features Distinguish the Angiosperms? Perfect flowers: have both mega- and microsporangia. Imperfect flowers: either mega or microsporangia. Monoecious: “one-housed”; male and female flowers occur on the same plant. Dioecious: “two-housed”; male and female flowers on different plants.

35. 29.3 What Features Distinguish the Angiosperms? If petals and sepals are indistinguishable, they are called tepals. Inflorescence: grouping of flowers. Different families have characteristic types.

36. Figure 29.10 Inflorescences (Part 1)

37. Figure 29.10 Inflorescences (Part 2)

38. 29.3 What Features Distinguish the Angiosperms? Flowers of the basal clades have many tepals, carpels, and stamens. Evolutionary change has modified this— reduction in numbers of floral organs, changes in symmetry, and fusion of parts.

39. Figure 29.11 Flower Form and Evolution

40. 29.3 What Features Distinguish the Angiosperms? Carpels and stamens may have evolved from modified leaves. Carpels became progressively more fused and buried in the receptacle tissue.

41. 29.3 What Features Distinguish the Angiosperms? Long styles in pistils and long filaments in stamens: length increases likelihood of pollination—either making them more accessible to insects, or to catch the wind.

42. 29.3 What Features Distinguish the Angiosperms? Perfect flowers: favors self-pollination, usually disadvantageous. Many mechanisms have evolved to circumvent this problem.

43. Figure 29.13 Stigma Behavior Increases Pollen Export in Monkeyflowers (Part 1)

44. 29.3 What Features Distinguish the Angiosperms? Most angiosperms are animal-pollinated— by insects, birds, and bats. Many flowers entice pollinators with nectar and pollen. Plants and their pollinators have coevolved; some relationships are very specific.

45. 29.3 What Features Distinguish the Angiosperms? Angiosperm life cycle: Zygote develops into an embryo: consists of an embryonic axis (will become stem and root), and 1 or 2 cotyledons—seed leaves. Cotyledons absorb and digest the endosperm, some become photosynthetic.

46. Figure 29.14 The Life Cycle of an Angiosperm

47. 29.3 What Features Distinguish the Angiosperms? Ovary and seeds develop into fruits. Fruit protects seed and aids in dispersal, (e.g., can become attached to or eaten by animals).

48. 29.3 What Features Distinguish the Angiosperms? Simple fruits develop from one carpel. Ex: cherry Aggregate fruits develop from several carpels. Ex: raspberry Multiple fruits form from a cluster of flowers. Ex: pineapple Accessory fruits develop from parts other than carpels plus the carpel. Ex: strawberry

49. Figure 29.15 Fruits Come in Many Forms and Flavors

50. 29.4 How Did the Angiosperms Originate and Diversify? Most angiosperms are in two clades: Monocots: one cotyledon Eudicots: two cotyledons Other clades include star anise and relatives, water lilies, and magnoliids.

51. Figure 29.18 Monocots

52. Figure 29.19 Eudicots

53. 29.5 How Do Plants Support Our World? Many medicines come from seed plants. Medicines are found by screening large numbers of plants, or screening large numbers of chemical compounds. Ethnobotanists also discover medicinal plants by studying people and their uses of plants all over the world.

54. Table 29.1