Chapter 29
Plant Diversity I:
The Colonization of Land
AP Biology
Requirements for
Successful Life on Land
 Supporting mechanism (vascular tissue,
lignin)
 Absorptive structures (above & below
ground)
 Conducting tissues (move fluids)
 Anti-desiccation (drying out) adaptations
for body of plant (cuticle) & gametes
(pollen & spores)
 Airborne gamete dispersal
General Characteristics of
Plants
 Includes mosses, ferns, conifers,
flowering plants
 Multicellular, eukaryotic, photosynthetic
autotroph
 Chlorophyll a, b, and carotenoids
 Cellulose
 Starch
General Characteristics of
Plants, cont.
 Alternation of generations (more next)
 Most have stomata for gas exchange
(Liverworts the exception)
 Secrete cuticle to reduce desiccation
 Most have vascular tissue for bulk transport of
water and materials
 Exchange of materials between adjacent cells
through opening in cell walls (plasmodesmata)
 Most have seeds (embryo with food &
protective covering)
Alternation of Generations
 Gametes produced &
protected within
gametangia (nonreproductive cells to
prevent desiccation & for
protection)
 Fertilization of egg takes
place here (Female =
archegonium; Male =
antheridium)
Alternation of
Generations, cont.
 Sporophyte & gametophyte are structurally
(look & develop) different (heteromorphic)
 Both structures are multicellular (unlike
animals)
 Sporophyte dominant in most species
 Meiosis in sporophyte produces haploid
reproductive cells (spores)
 Spores can develop into a new organism
without fusing with another cell
Proposed Ancestors of
Plants
 Charophyceans are the green algae most related
to land plants
 Several lines of evidence support this including:
 Homologous chloroplasts, cell walls,
peroxisomes, sperm
 Phragmoplasts – microtubules form perpendicular
to cell plate and guide deposition of cellulose to
form wall
 Molecular systematics
 Charophyceans had a layer of sporopollenin to
prevent exposed zygotes from drying out until
they are in water again
Classified Into 2 Major
Groups
1. Nonvascular plants
(aka Bryophytes)



Bryophyta: mosses
Anthocrophyta: Hornworts
Heptophyta: Liverworts
2. Vascular Plants (aka Tracheophytes)

Seedless vascular plants (Pteridophytes)


Lycophyta: Lycophytes
Pterophyta: Ferns & Horsetails
 Seeded vascular plants
 Naked seeded plants
(Gymnosperms)




Coniferophyta: Conifers
Cycadophyda: Cycads
Gnetophyta: Gnetae
Ginkgophyta: Ginko
 Flowering plants and
enclosed seeds
(Angiophyta)
 Flowering plants
Nonvascular Plants:
Bryophytes
 Gametophyte dominant form
 Lack vascular tissues
 Limits size (can’t grow tall)
 Rely on diffusion
 Rhizoids – analogous to roots; used for anchorage
 Male flagellated sperm produced by the gametangium
(antheridium)
 Female egg produced by the gametangium (archegonium)
 Sporophyte produces haploid spores within sporangium
 3 Divisions:
 Bryophyta (mosses); ex: Sphagnum (peat moss)
 Heptophyta (Liverworts); sexual and asexual reproduction
 Anthocerophyta (hornworts)
Vascular Plants:
Tracheophytes
 Key adaptations to success on
land:
 Seeds – protect embryo & provide
food for initial growth
 Pollen – airborne dispersal;
Sporopollenin in walls of spores
 Sporophyte dominant
 Vascular tissues – phloem &
xylem; specialization of parts of
plant for specific functions (true
roots, stems, and leaves)
 Ligninfied cell walls – supports
plant in air
Seedless Vascular Plants
 Division Lycophyta
 Club mosses
 Many are epiphytes – grow on other
plants but not parasitic
 Sporangia produced on specialized
leaves for reproduction called
sporophylls
 Most species are homosporous –
produce a single type of spore that can
produce a gametophyte with antheridia
and archegonia
 Heterosporous species – have
sporophytes that produce separate
spores
 Megaspores – produce female
archegonia on female gametophyte
 Microspores – produce male antherdia on
male gametophyte
Seedless Vascular Plants
 Division Sphenophyta
 Horsetail (Equisetum) – only
extant genus
 Homosporous
 Silica in cell walls make
stems abrasive
 Gametophyte is free-living;
can photosynthesize and
not dependent on
sporophyte for nutrients
Seedless Vascular Plants
 Division Pterophyta
 Ferns – dominant seedless vascular
plant
 Large leaves (fronds) – compound
with smaller leaflets
 Leaves are megaphylls – leaves
with branched vascular tissues/veins
 Homosporous
 Sporangia develop on specialized
sporophylls
 Sporangia grow in clusters (sori) on
underside
 Flagellated sperm – require water &
fertilization of egg in archegonium
 Sporophyte protected in
archogonium and emerges from
ground as fiddlehead