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. The General Plant Life Cycle
process

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 ,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. Ulva life cycle
MITOSIS

14. Charophytes Charophytes are green algae related to land plants

15. Charophytes Charales (300 species) Choleocaetales (30 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”
Ovule is 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 is Amborella

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 called whorls

47. Angiosperms Flower morphology Outermost whorl = Sepals
Second whorl = Petals
Third whorl = 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. The ovary eventually develops into the plant’s fruit
Angiosperms
The ovary eventually develops into the plant’s fruit

49. Angiosperm Reproduction