Chapter 29
Plant Diversity I:
How Plants Colonized Land
Characteristics
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photoautotrophic mulitcellular eukaryotes
cellulose cell walls
store carbohydrates as starch
chlorophyll a, b, & carotenoids
mitosis & meiosis
Plant Evolution
Evolution
• 400 mya, plants colonized land
• gametangia – jacketed sex organs evolved
and protected gametes, embryos from
desiccation
• heteromorphic alternation of generations
• sporophyte more conspicuous, except in
bryophytes
• followed changes in terrestrial conditions
Gametangia
Adaptations to land
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gametangia
seeds
cuticle
stomata
vascular tissue (xylem & phloem)
lignin – supports cellulose matrix
Major periods in plant evolution
1) terrestrial adaptations allowed plants to
move from water (algae) to land ~ 400 mya
2) vascular tissue evolved
3) origin of the seed ~ 260 mya allowed embryos
to leave the parent plant encased in a
resistant coat with food supply
4) evolution of flower ~ 130 mya (specialized
reproductive structure producing ovaryenclosed seeds)
Ancestry
• evolved from Chlorophyta (green algae), more
specifically Charophyceans with chl. a &
accessory pigments, cellulose cell walls, store
starch, form cell plates in cytokinesis
• divergence from common ancestry or separate
origins from different algae types resulted in
vascular & nonvascular (hornworts, liverworts,
mosses) plants
• trend toward increasing dominance of diploid
sporophyte in vascular plants
Classification
Nonvascular plants:
-no true roots, stems, leaves
Division Bryophyta – hornworts, liverworts,
mosses
~ 16, 000 species
- lack many terrestrial adaptations
- low-growing, require damp, shady places
Bryophytes
Classification
Vascular plants: (Tracheophytes)
- true roots, stems, leaves
Seedless plants
Division Psilophyta – whiskferns
~ 10 – 13 species
- ex: Psilotum
Classification
Division Lycophyta – club mosses
~ 1,000 species
- may be epiphytic – grow on substrates, but
are not parasites
- have sporophylls – leaves specialized for
reproduction
- ex: Lycopodium
homosporous – have both M & F sex organs
produce a single type of spore
heterosporous – 2 types of spores
megaspores – develop into female
gametophytes
microspores – develop into male
gametophytes
Classification
Division Sphenophyta – horsetails
~ 15 species
- ex: Equisetum
Division Pterophyta – ferns
~ 12,000 species
- microphylls – leaves arising from stem with
singular vascular tissue
- megaphylls – branched system of veins
Seedless vascular plants
Chapter 30
Plant Diversity II:
The Evolution of Seed
Plants
Classification
Seeded plants
Gymnosperms – “naked seed” plants
Division Coniferophyta – cone bearers
~ 550 species
- leaves are modified as needles
- transport water in tracheids – primitive,
tapered cells which function in mechanical
support
- ex: Pinus, sequoia, fir, spruce
Pollen cones
Pine seed
Classification
Division Cycadophyta – cycads
~ 100 species
- bear naked seeds on scales
- ex: sago palm
Division Ginkgophyta – ginkgoes
- 1 species
- resistant to pollution
- ex: Ginkgo biloba
Sago palm (cycad)
Classification
Division Gnetophyta
~ 70 species
ex: Gnetina, Welwitschia
Classification
Angiosperms – “flowering plants”
~ 235,000 species
Division Anthophyta
Class Monocotyledonae – monocots
- one cotyledon (embryonic seed leaf)
- parallel venation in leaves
- vascular bundles scattered in stem
- flower parts in 3’s
- ex: grasses, lilies
* vessel elements, fiber cells
Angiosperms
Flower anatomy
• Fruit – mature ovary
• Seed – mature ovule
Tracheids and vessel elements
Classification
Class Dicotyledonae – dicots
- 2 cotyledons
- branched venation
- vascular bundles in a ring
- flower parts in 4’s or 5’s
*Double fertilization – characteristic of Angiosperms
(prevents squandering of nutrients), also evolved
independently in some gymnosperms
Pollinators