1. Plant Diversity I How Plants Colonized Land
Chapter 29
Plant Diversity I How Plants Colonized Land

3. Concept 29.1: Land plants evolved from green algae
Green algae called charophyceans are the closest relatives of land plants

4. Morphological and Biochemical Evidence
Four key traits only with charophyceans:
Rose-shaped complexes for cellulose synthesis
Peroxisome enzymes
Structure of flagellated sperm
Formation of a phragmoplast

6. Coleochaete orbicularis, a disk-shaped charophycean (LM).
Chara,
a pond
organism
(LM).
10 mm
40 µm
Coleochaete orbicularis, a disk-shaped
charophycean (LM).

7. Advantages to Living on Land
Increased sunlight unfiltered by water
More Carbon Dioxide available
Soil Rich in Nutrients
Fewer Predators

8. Problems to Overcome Lack of water Dessication
SPOROPOLLENIN: polymer prevents spores from drying out.
CUTICLE: waxy layer on epidermis
Lack of structural support against gravity

9. Derived Traits of Plants
Five key traits appear in nearly all land plants but are absent in the charophyceans:
Apical meristems
Alternation of generations
Walled spores produced in sporangia
Multicellular gametangia
Multicellular dependent embryos

10. Apical Meristems LE 29-5a Apical Meristem of shoot Developing leaves
Root
100 µm
100 µm

11. Alternation of Generations
LE 29-5b
Alternation of Generations
Haploid multicellular
organism (gametophyte)
Mitosis
Mitosis
Spores
Gametes
MEIOSIS
FERTILIZATION
Zygote
Mitosis
Diploid multicellular
organism (sporophyte)

13. ALTERNATION OF GENERATIONS
HAPLOID GAMETOPHYTE undergoes MITOSIS to produce 1n Gametes (Sperm or Egg)
FERTILIZATION to make DIPLOID ZYGOTE
ZYGOTE develops into DIPLOID SPOROPHYTE
SPOROPHYTE (2n) undergoes MEIOSIS to produce HAPLOID SPORES
SPORES (1n) develop into HAPLOID GAMETOPHYTE
SPORES are produced in SPORANGIA

14. ALTERNATION OF GENERATIONS continued.
GAMETANGIA: multicellular organs in which gametes are produced.
MALE gametangia= ANTHERIDIA- make sperm
FEMALE gametangia = ARCHEGONIUM- make
single egg

15. Walled Spores Produced in Sporangia Multicellular Gametangia
LE 29-5c
Walled Spores
Produced in Sporangia
Multicellular
Gametangia
Multicellular,
Dependent Embryos
Longitudinal section of
Sphagnum sporangium (LM)
Archegonium
with egg
Female gametophyte
Spores
Embryo
Maternal
tissue
Sporangium
2 µm
10 µm
Sporophyte
Male gametophyte
Antheridium
with sperm
Gametophyte
Wall
ingrowths
Placental
transfer
cell
Sporophyte and sporangium
of Sphagnum (a moss)
Archegonia and antheridia
of Marchantia (a liverwort)

16. Additional derived traits such as a cuticle and secondary compounds evolved in many plant species

18. 4 Main GROUPS OF PLANTS: Seedless Nonvascular Seedless Vascular
Vascular with Naked Seeds
Vascular with Seeds
*** Vascular Plants - Tracheophytes

19. Seedless vascular plants Origin of vascular plants
Land plants
Vascular plants
Bryophytes
Seedless vascular plants
Seed plants
Gymno-
sperms
Angio-
sperms
Liverworts
Hornworts
Mosses
Lycophytes
Pterophytes
Charophyceans
Origin of seed plants
(about 360 mya)
Origin of vascular plants
(about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga

20. 1) Seedless Non Vascular (no xylem or phloem)
Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants:
Liverworts, Hornworts, Mosses,

21. Bryophyte Gametophytes
In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes
Sporophytes are typically present only part of the time
Animation: Moss Life Cycle

22. LE 29-8 Raindrop Key Male gametophyte Haploid (n) Sperm Diploid (2n)
Spores develop into
threadlike protonemata.
“Bud”
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.
Antheridia
The haploid protonemata produce “buds” that grow into gametophytes.
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.
Protonemata
“Bud”
Egg
Spores
Gametophore
Female
gametophyte
Archegonia
Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.
Rhizoid
Peristome
Sporangium
The sporophyte grows a long stalk, or seta, that emerges from the archegonium.
FERTILIZATION
MEIOSIS
(within archegonium)
Seta
Calyptra
Capsule
(sporangium)
Zygote
Mature
sporophytes
Foot
Embryo
Archegonium
The diploid zygote develops into a sporophyte embryo within the archegonium.
Young
sporophyte
Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
Capsule with
peristome (SEM)
Female
gametophytes

23. Bryophyte gametophytes
Produce flagellated sperm in antheridia
Produce ova in archegonia
Generally form ground-hugging carpets and are at most only a few cells thick
Some mosses have conducting tissues in the center of their “stems” and may grow vertically

24. Bryophyte Sporophytes
Grow out of archegonia
Are the smallest and simplest of all extant plant groups
Consist of a foot, a seta, and a sporangium
Hornwort and moss sporophytes have stomata

25. Marchantia polymorpha, a “thalloid” liverwort
LE 29-9a
Gametophore of
female gametophyte
500 µm
Foot
Seta
Sporangium
Marchantia polymorpha,
a “thalloid” liverwort
Marchantia sporophyte (LM)

26. LE 29-9b
Plagiochila
deltoidea,
a “leafy”
liverwort

27. LE 29-9c
An Anthroceros
hornwort species
Sporophyte
Gametophyte

28. LE 29-9d
Polytrichum
commune,
hairy cap
moss
Sporophyte
Gametophyte

29. 2. Seedless Vascular Plants
Pteridoyphytes: (Ferns, Club Mosses, Horsetails)
DOMINANT SPOROPHYTE
(grows from the gametophyte)
Mature sporophyte independent
FLAGELLATED SPERM (need water to swim)
Animation: Fern Life Cycle

30. LE 29-12 Key Haploid (n) Diploid (2n) Antheridium Spore Young
gametophyte
Antheridium
MEIOSIS
Sporangium
Sperm
Archegonium
Egg
New
sporophyte
Sporangium
Mature
sporophyte
Zygote
FERTILIZATION
Sorus
Gametophyte
Fiddlehead

31. 3. VASCULAR PLANTS (naked seed and covered seed)
Vascular plants have two types of vascular tissue: xylem and phloem
Xylem conducts most of the water and minerals and includes dead cells called tracheids
Phloem consists of living cells and distributes sugars, amino acids, and other organic products
Roots
anchor vascular plants
absorb water and nutrients from the soil

32. VASCULAR STRUCTURES continued
Leaves :
increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

33. Leaves are categorized by two types:
Microphylls, leaves with a single vein
Megaphylls, leaves with a highly branched vascular system
According to one model of evolution, microphylls evolved first, as outgrowths of stems

34. LE 29-13
Vascular tissue
Microphylls
Megaphylls

35. Sporophylls and Spore Variations
Sporophylls are modified leaves with sporangia
Homospory (Homosporous)
Most seedless vascular plants
One type of spore that forms a bisexual gametophyte
Heterospory (Heterosporous)
All seed plants and some seedless vascular
2 Types of spores (one male/ one female)

37. Classification of Seedless Vascular Plants
There are two phyla of seedless vascular plants:
Lycophyta includes club mosses, spike mosses, and quillworts
Pterophyta includes ferns, horsetails, and whisk ferns and their relatives

38. LE 29-14a
Selaginella apoda,
a spike moss

39. LE 29-14b
Isoetes
gunnii,
a quillwort

40. Diphasiastrum tristachyum, a club moss
LE 29-14c
Strobili
(clusters of
sporophyllis)
Diphasiastrum tristachyum, a club moss

41. LE 29-14d
Psilotum
nudum,
a whisk
fern

42. Equisetum arvense, field horsetail Vegetative stem Strobilus on
LE 29-14e
Equisetum
arvense,
field
horsetail
Vegetative stem
Strobilus on
fertile stem

43. Athyrium filix-femina, lady fern
LE 29-14f
Athyrium filix-femina, lady fern