Diversity: The Origin and Evolution of the Land Plants 19 February, 2010

1. Diversity: The Origin and Evolution of the Land Plants 19 February, 2010

2. Life on Earth Depends on the Land Plants

3. Plant Diversity I. How many species of land plants are there? II. Evolution of the Land Plants  III. Derived Traits of the Land Plants • IV. Major Lineages of Land Plants • Cooksonia was the first vascular plant. It appeared some 425 MY ago. B. The evolutionary tree of vascular plants has three main branches. 

4. Plant Diversity Q. How many species of land plants are there, worldwide? A. Estimates vary, but probably around 315,000 species Q. How many plant species in Vermont? A. Just over 2,000 species

5. Plant Diversity I. How many species of land plants are there? II. Evolution of the Land Plants III. Derived Traits of the Land Plants • IV. Major Lineages of Land Plants • Cooksonia was the first vascular plant. It appeared some 425 MY ago. B. The evolutionary tree of vascular plants has three main branches. 

6. The ancestors of the land plants were marine algae...

7. Fig. 29-4 Red algae ANCESTRAL ALGA Chlorophytes Viridiplantae Charophytes Streptophyta Plantae Embryophytes

8. Chara, an alga in the division Charophyta

9. Charophyta (charophytes) Divisions of Algae

10. The charophytes (Division Charophyta) share the following features with the land plants: • Chlorophyll A& B • Storage product = starch • Cell walls = cellulose • Phragmoplast • DNA sequences

11. Development of a land flora possible only after the development of an ozone (O3) layer to shield against UV radiation. Where did the ozone come from? Oxygen accumulated in the early atmosphere as the result of photosynthesis carried out by marine algae. Electrical discharge transformed O2 into O3.

12. The Geologic Timetable Appearance of the land plants < Ordovician, ca. 475 mybp

13. Clicker Question Which of the following factors differ between the aquatic and the terrestrial environments? • CO2 concentration • Spatial distribution of water and nutrients • Physical support provided to the plant • The light environment • All of the above

14. The ancestors of the land plants were adapted to life in an aqueous environment • Resources were uniformly distributed • Plants didn’t have to stand up against gravity

15. Things were different on land!

16. What structural and biochemical adaptations facilitated life on land? • Cuticle • Stomates • Secondary metabolites, particularlylignin • Sporopollenin • Mycorrhizal fungi • Roots • Internal transport system

17. Cuticle (water loss) and stomates (gas exchange)

18. Lignin and other secondary metabolites structure of lignin tracheids with lignified 2o walls

19. Sporopollenin (resistant spore coat)

20. Mycorrhizal fungi

21. Root System (anchorage & absorption)

22. Internal transport system (xylem & phloem) phloem xylem

23. Plant Diversity I. How many species of land plants are there? II. Evolution of the Land Plants  III. Derived Traits of the Land Plants • IV. Major Lineages of Land Plants • Cooksonia was the first vascular plant. It appeared some 425 MY ago. B. The evolutionary tree of vascular plants has three main branches. 

24. Derived Traits of Land Plants Four key traits appear in nearly all land plants but are absent in the charophytes: • Alternation of generations (with multicellular, • dependent embryos) • Walled spores produced in sporangia • Multicellular gametangia • Apical meristems

25. Fig. 29-5a Gamete from another plant Gametophyte (n) Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION Zygote 2n Mitosis Sporophyte (2n) Alternation of generations

26. Derived Traits of Land Plants Four key traits appear in nearly all land plants but are absent in the charophytes: • Alternation of generations (with multicellular, • dependent embryos) • Walled spores produced in sporangia • Multicellular gametangia • Apical meristems

27. Trilete spores of Lycopodium

28. The kidney-shaped sporangia of clubmoss

29. Lycopodium strobilus, with close-up of sporangia

30. Derived Traits of Land Plants Four key traits appear in nearly all land plants but are absent in the charophytes: • Alternation of generations (with multicellular, • dependent embryos) • Walled spores produced in sporangia • Multicellular gametangia • Apical meristems

31. The heart-shaped gametophyte of many ferns

32. Fern gametophyte, with antheridia and archegonia

33. Antheridia and archegonia, fern gametophyte, 400x

34. Derived Traits of Land Plants Four key traits appear in nearly all land plants but are absent in the charophytes: • Alternation of generations (with multicellular, • dependent embryos) • Walled spores produced in sporangia • Multicellular gametangia • Apical meristems

35. Fig. 29-5e Apical meristems Developing leaves Apical meristem of shoot Apical meristem of root Shoot Root 100 µm 100 µm

36. Plant Diversity I. How many species of land plants are there? II. Evolution of the Land Plants   III. Derived Traits of the Land Plants • IV. Major Lineages of Land Plants • Cooksonia was the first vascular plant. It appeared some 425 MY ago. B. The evolutionary tree of vascular plants has three main branches. 

37. The Geologic Timetable <Silurian, Ca. 425 mybp

38. Cooksonia, the first vascular plant

39. Plant Diversity I. How many species of land plants are there? II. Evolution of the Land Plants   III. Derived Traits of the Land Plants • IV. Major Lineages of Land Plants • Cooksonia was the first vascular plant. It appeared some 425 MY ago. B. The evolutionary tree of vascular plants has three main branches. 

40. Vascular Plants Plants with true leaves The Lycophytes: spore-dispersed plants with microphylls Seed Plants Ferns and friends Clubmosses and friends microphylls megaphylls spore-dispersed

41. Clubmoss Shining clubmoss Ground cedar

42. Spike moss (Selaginella sp.)

43. The Geologic Timetable < Carboniferous

44. The Carboniferous coal swamp forest reconstructed. These were among Earth’s first forests.

45. Lepidodendron - the scale tree of the Carboniferous coal swamp

46. The remains of the Carboniferous scale trees form the great coal deposits of the world

47. Clicker Question A feature unique to the Lycophytes among the spore-dispersed vascular plants is the presence of: • Roots • Leaves • Microphylls • Megaphylls • Xylem and phloem

48. Vascular Plants The Monilophytes: spore-dispersed plants with true leaves (megaphylls) Seed Plants Ferns and friends Clubmosses and friends megaphylls

49. Ferns - the second-most diverse group of vascular plants ca. 12,500 species