Plant Diversity I:
The Colonization
of
Land
Campbell, 5th Edition, Chapter 29
Nancy G. Morris
Volunteer State Community College
Figure 29.3
Highlights of Plant Evolution
Review of Characteristics:

Chloroplasts with photosynthetic
pigments: chlorophyll a, chlorophyll b,
carotenoids

Cell walls containing cellulose
–
Secondary cell walls containing lignin

Food stored as amylose in plastids

Classification of Kingdom (Table 29.1)
Plant Kingdom



Members show structural, chemical, &
reproductive adaptations of terrestrial life
This distinguishes higher plants from the
aquatic algae
Structural adaptation includes specialized
structures to obtain water, minerals,
carbon dioxide, light, etc.
– Example: stomata – special pores on
surface for gas exchange
Plant Kingdom



Chemical adaptation includes a waxy cuticle,
composed of cutin, to prevent desiccation
Cutin, lignin, sporopollenin are examples of
secondary products meaning that they are
produced through metabolic pathways not
common to all plants
cellulose is an example of a primary product
Plants as Embryophytes
A new mode of reproduction was
necessary to move from an aquatic to
terrestrial existence:

1) Gametes are produced in gametangia,
organs with protective jackets of sterile
cells that prevent gametes from drying
out. Egg is fertilized within the female
organ.
Figure 29.1a
Plants as Embryophytes

2) Embryos must be protected against
desiccation. Zygote develops into embryo
that is retained within female protective
cells in the gametangia
Figure 29.1b
Alternation of Generations: a review



All higher green plants reproduce
sexually
Most are also capable of asexual
reproduction
The haploid gametophyte generation
produces and alternates with a diploid
sporophyte generation. The sporophyte
produces gametophytes.
Figure 29.2
Alternation
of
Generation
Alternation of Generations: a review



The life cycle is heteromorphic – the
gametophyte & sporophyte differ in
morphology
The sporophyte is larger & more
noticeable in all but the bryophytes
Reduction of the gametophyte and
dominance of the sporophyte generation
we move from bryophytes to angiosperms
Figure 29.5 Hypothetical Mechanism:
Origin of Alternations of Generations
Keeping a low profile…
Bryophytes:



Lack woody tissue
Unable to support tall plants on land
Often sprawl horizontally as mats
Nonvascular Plants: 3 Divisions
Bryophyta
Mosses
Sphagnum
Hepatophyta
Liverworts
Marchantia
Anthocerophyta
Hornworts
Division Bryophyta





Bryon (Gr. “moss”)
Grip substratum with rhizoids
Cover about 3% of land surface
Contain vast amounts of organic carbon
Campbell, Figure 29.7, Life Cycle of a
Moss
Division Hepatophyta




Liverworts
Sporangia have elaters, coil-shaped cells,
that spring out of capsule & disperse
spores
Also reproduce asexually from gemmae
(small bundles of cells that bounce out of
cups when hit by rainwater)
Campbell, Figure 29.8
Division Anthocerophyta




Hornworts
Resemble liverworts but sporophyte
is horn-shaped
Photosynthetic cells have one large
single chloroplast
Campbell, Figure 29.9
Adaptation to land




Antheridium produces flagellated
sperm
Archegonium produces a single egg
Fertilization occurs within the
archegonium
Zygote develops into an embryo
within the archegonium
(embryophyte condition)
Ancestral aquatic habitat evident…




Water required for reproduction
Flagellated sperm cells swim from the
antheridium to the archegonium
Vascular tissue is absent
Water is distributed throughout the plant
by the relatively slow process of diffusion,
capillary action, cytoplasmic streaming
Six terrestrial adaptations:
1) Regional specialization of the
plant body:
 subterranean roots that absorb
water & minerals from the soil
 aerial shoot system of stems &
leaves to make food
Terrestrial adaptations:
2) Structural support
–
support is provided by lignin
embedded into the cellulose
matrix of cell walls
Terrestrial adaptations:
3)


Vascular systems evolved:
XYLEM – complex tissue that conducts
water & minerals from the roots to the
rest of the plant; composed of dead,
tube-shaped cells that form a microscopic
water-pipe system
PHLOEM – conducts sugars, amino acids,
etc. throughout the plant; composed of
living cells arranged in tubules
Terrestrial adaptations:



4) Pollen – pollination
eliminated the need for water to
transport gametes
5) Seeds
6) Increased dominance of the
diploid sporophyte
Vascular plants display two
distinct reproductive strategies:

Homosporous plants produce one type of spore
–

Each spore develops into a bisexual gametophyte with
both antheridia and archegonia
Heterosporous plants produce two kinds of spores:
– Megaspores develop into female gametophytes
possessing archegonia
–
Microspores develop into male gametophytes
possessing antheridia
Comparison
Homosporous
Sporophyte
Heterosporous
Sporophyte
Single
type of
spore
Megaspore
Microspore
Eggs
Bisexual
gametophyte
Female
Gametophyte
Male
Gametophyte
Sperm
Eggs
Sperm
Seedless vascular plants:
primitive tracheophytes

Division Psilophyta - whisk ferns

Division Lycophyta - club mosses

Division Sphenophyta - horsetails

Division Pterophyta - ferns
Division Lycophyta





Club mosses (Fig. 29.12)
Sporangia are borne on sporophylls – leaves
specialized for reproduction
In some sporoangia, sporophylls are clustered at
branch tips into club-shaped strobili – hence the
name club moss
Spores develop into inconspicuous gametophytes
that are nurtured by symbiotic fungi.
Most are homosporous. (Selaginella is
heterosporous.)
Division Sphenophyta


(Fig. 29.13) Equisetum
Common in Northern Hemisphere
in damp locations

Homosporous

Gametophyte is only a few mm

Gametophyte is free-living &
photosynthetic
Division Pterophyta: FERNS





12,000 existing species
most ferns have fronds
homosporous
sori on underside of leaf with annulus
to catapult spores into the air
prothallus (gametophyte) requires
water
Figure 29.11
Life Cycle of a Fern
“Coal forests”



During the Carboniferous period, the
landscape was dominated by extensive
swamp forests: club mosses, whisk ferns,
horsetails were gigantic plants
Organic rubble of the seedless plants
accumulated as peat (Figure 29.14)
When later covered by sea and sediment,
heat & pressure transformed the peat
into coal