Overview of Green Plants

1. Overview of Green Plants Chapter 30

2. Defining Plants • The kingdom Viridiplantae includes land plants and green algae • Red and brown algae are excluded • The green algae split into two major clades • Chlorophytes • Charophytes • Streptophyta includes the Charophytes and all land plants • All green plants arose from a single species of freshwater algae

3. Defining Plants

4. Defining Plants • Land plants have two major features • Protected embryos • Multicellular haploid and diploid phases

5. Defining Plants Adaptations to terrestrial life • Evolution of leaves that increase photosynthetic surface area • Protection from desiccation by a waxy cuticle and stomata • Shift to a dominant vertical diploid generation

6. Plant Life Cycles • Humans have a diplontic life cycle • Only the diploid stage is multicellular Plants have a haplodiplontic life cycle • Multicellular diploid stage = Sporophyte • Multicellular haploid stage = Gametophyte • Plants have an alternation of generation • sporophyte → gametophyte → sporophyte → etc.

7. Plant Life Cycles • Sporophyte (2N) produces haploid spores (N) by meiosis • Spores (N) divide by mitosis producing the gametophyte (N) • Gametophyte (N) produces gametes (N) by mitosis • Gametes (N) fuse to form the diploid sporophyte (2N)

8. process process process The General Plant Life Cycle

9. Plant Life Cycles As more complex plants evolved: • Diploid stage (sporophyte) became the dominant portion of the life cycle • Gametophyte became more limited in size • Sporophyte became nutritionally independent

10. Chlorophytes • Chlorophytes, sister taxa of the Streptophytes, are a diverse group including: • Chlamydomonas • Unicellular chlorophyte with two flagella • Have eyespots to direct swimming • Reproduces asexually as well as sexually

11. Chlorophytes • Volvox • Colonial chlorophyte • Hollow sphere of a single layer of 500-60,000 cells • A few cells are specialized for reproduction

12. Chlorophytes • Ulva • Multicellular chlorophyte • True haplodiplontic life cycle • Gametophyte and sporophyte have identical appearance

13. MITOSIS Ulva life cycle

14. Charophytes • Charophytes are green algae related to land plants Land plants

15. Charophytes • Charales (300 species) • Macroscopic • Plant-like plasmodesmata • Sister clade to land plants • Choleocaetales (30 species) • Microscopic • Plant-like mitosis • Next closest plant relatives

16. Bryophytes • Bryophytes are the closest living descendants of the first land plants • Called nontracheophytes because they lack tracheids (specialized transport cells) • Simple, but highly adapted to diverse terrestrial environments • Non-photosynthetic sporophyte is nutritionally dependent on the gametophyte • 3 groups: liverworts, hornworts and mosses

17. Bryophytes • Liverworts (phylum Hepaticophyta) • Have flattened gametophytes with liver-like lobes • Form gametangia in umbrella-shaped structures • Also undergo asexual reproduction

18. Bryophytes • Hornworts (phylum Anthocerotophyta) • Sporophyte has stomata • Sporophyte is photosynthetic • Cells have a single large chloroplast

19. Bryophytes • Mosses (phylum Bryophyta) • Gametophytes consist of small, leaflike structures around a stemlike axis • Anchored to substrate by rhizoids • Multicellular gametangia form at the tips of gametophytes • Archegonia – Female gametangia • Antheridia – Male gametangia • Mosses withstand drought, but not air pollution

20. Moss Reproduction

21. Tracheophyte Plants • Cooksonia, the first vascular land plant, appeared about 420 MYA • Only a few centimeters tall • No roots or leaves • Homosporous (spores are the same size and type)

22. Tracheophyte Plants • Vascular tissues are of two types • Xylem – Conducts water and dissolved minerals upward from the roots • contains tracheids • Phloem – Conducts sucrose and hormones throughout the plant • These enable enhanced height and size in the tracheophytes • Tracheophytes are also characterized by the presence of a cuticle and stomata

23. Tracheophyte Plants • Vascular plants have gametophytes reduced in size and complexity relative to sporophytes • Seeds • Highly-resistant structures that protect the plant embryo • Occur only in heterosporous plants • Fruits in flowering plants add a layer of protection to seeds • Also attract animals that disperse seeds

24. Tracheophytes • Vascular plants(tracheophytes)include seven extant phyla grouped in three clades • Lycophytes (club mosses) • Pterophytes (ferns and their relatives) • Seed plants

25. Lycophytes • Club mosses are the earliest vascular plants • They lack seeds • Superficially resemble true mosses but they are not related • Homosporous or heterosporous

26. Pterophytes • The phylogenetic relationships among ferns and their relatives is still being sorted out

27. Pterophytes • Whisk ferns • Saprophyte consists of evenly forking green stems without leaves or roots • Some gametophytes develop elements of vascular tissue • Often symbionts with fungi

28. Pterophytes • Horsetails • All 15 living species are homosporous • Constitute a single genus, Equisetum • Consist of ribbed, jointed photosynthetic stems that arise from branching rhizomes • High silica content in stems made them useful as “scouring rushes”

29. Pterophytes • Ferns • The most abundant group of seedless vascular plants with about 11,000 species • The conspicuous sporophyte and much smaller gametophyte are both photosynthetic

30. Pterophytes • The fern life cycle differs from that of a moss • Much greater development, independence and dominance of the fern’s sporophyte • Fern morphology • Sporophytes have rhizomes • Fronds (leaves) develop at the tip of the rhizome as tightly rolled-up coils then uncoil and expand

31. Pterophytes Uncoiled fronds are called “fiddleheads” and are a delicacy among northern First Nation peoples

32. Pterophytes

33. Pterophytes • Fern reproduction • Most fern are homosporous • Produce distinctive sporangia in clusters called sori on the back of the fronds • Diploid spore mother cells in sporangia produce haploid spores by meiosis • At maturity, the spores are catapulted by snapping action

34. Seed Plants • Seed plants first appeared 305-465 MYA • Evolved from spore-bearing plants known as progymnosperms • The seed represents an important advance • Protects the embryo • Easily dispersed • Introduces a dormant phase in the life cycle

35. Seed Plants • Seed plants produce 2 kinds of gametophytes • Male gametophytes • Pollen grains • Dispersed by wind or a pollinator • Female gametophytes • Develop within an ovule • Enclosed within diploid sporophyte tissue

36. Seed Plants • There are two types of seed plants • Gymnosperms are plants with “naked seeds” • Ovuleis exposed on a scale at pollination • All lack flowers and fruits of angiosperms • Angiosperms are flowering plants • Ovules are enclosed in diploid tissue at pollination • The carpel (modified leaf) covers seeds and develops into fruit

37. Gymnosperms • There are four living groups • Cycadophytes • Gnetophytes • Ginkgophytes • Coniferophytes

38. Gymnosperms • Cycads (phylum Cycadophyta) • Slow-growing gymnosperms of tropical and subtropical regions • Sporophytes resemble palm trees • Have largest sperm cells of all organisms!

39. Gymnosperms • Gnetophytes (phylum Gnetophyta) • Only gymnosperms with vessels in their xylem • Contain three (unusual) genera • Welwitschia • Gnetum • Ephedra • ephedrine can be extracted from species of this genus

40. Gymnosperms • Ginkgophytes (phylum Ginkgophyta) • Only one living species remains • Ginkgo biloba • Dioecious • Male and female reproductive structures form on different trees

41. Gymnosperms • Conifers (phylum Coniferophyta) are the largest gymnosperm phylum and include: • Pines, spruces, firs, cedars and others • Coastal redwood – Tallest tree • Bristlecone pine – Oldest living tree • Conifers are sources of important products • Timber, paper, resin and taxol (anti-cancer)

42. Gymnosperms • Pines • More than 100 species, all in the Northern hemisphere • Produce tough needlelike leaves in clusters • Leaves have: • Thick cuticle and recessed stomata • Canals into which cells secrete resin

43. Pine reproduction

44. Angiosperms • Angiosperm origins are a mystery • The oldest known angiosperm in the fossil record is Archaefructus • The closest living relative to the original angiosperm isAmborella

45. Angiosperms

46. Angiosperms • Flower morphology • Primordium develops into a bud at the end of a stalk called the pedicel • Pedicel expands at the tip to form a receptacle,to which other parts attach • Flower parts are organized in circles calledwhorls

47. Angiosperms • Flower morphology • Outermostwhorl = Sepals • Secondwhorl = Petals • Thirdwhorl = Stamens(androecium) • Each stamen has a pollen-bearing anther and a filament (stalk) • Innermost whorl = Gynoecium • Consists of one or more carpels that house the female gametophyte

48. Angiosperms The ovary eventually develops into the plant’s fruit

49. Angiosperm Reproduction