Chapter 29
Plant Diversity I
How Plants Colonized Land
Plants vs. Algae
•
Land plants evolved from Charophytes (Chara)
green algae
• 4 key traits plants share with Charophytes
(Morphological and Biochemical Evidence):
1. Rose-shaped complexes for cellulose synthesis
2. Peroxisome enzymes
3. Structure of flagellated sperm
4. Formation of a phragmoplast
5 key traits in nearly all land plants but are absent in
the charophytes:
1. apical meristems
2. multicellular dependent embryos
3. alternation of generations
4. walled spores produced in sporangia
5. multicellular gametangia
females – archegonia & males – antheridia
Fig. 29-5e
Apical
meristem
of shoot
Shoot
Developing
leaves
100 µm
Apical meristems
Apical meristem
of root
Root
100 µm
Fig. 29-5b
2 µm
Embryo
Maternal tissue
Wall ingrowths
10 µm
Placental transfer cell
(outlined in blue)
Embryo (LM) and placental transfer cell (TEM)
of Marchantia (a liverwort)
Fig. 29-5a
Gametophyte
(n)
Mitosis
n
n
Spore
Gamete from
another plant
Mitosis
n
n
Gamete
MEIOSIS
FERTILIZATION
2n
Mitosis
Sporophyte
(2n)
Alternation of generations
Zygote
Fig. 29-5c
Spores
Sporangium
Longitudinal section of
Sphagnum sporangium (LM)
Sporophyte
Gametophyte
Sporophytes and sporangia of Sphagnum (a moss)
Fig. 29-5d
Female gametophyte
Archegonium
with egg
Antheridium
with sperm
Male
gametophyte
Archegonia and antheridia of Marchantia (a liverwort)
Fig. 29-7
1 Origin of land plants (about 475 mya)
2 Origin of vascular plants (about 420 mya)
3 Origin of extant seed plants (about 305 mya)
Hornworts
1
Mosses
Pterophytes (ferns,
horsetails, whisk ferns)
3
Angiosperms
450
400
350
300
Millions of years ago (mya)
50
0
Seed plants
Gymnosperms
Vascular plants
2
Seedless
vascular
plants
Lycophytes (club mosses,
spike mosses, quillworts)
500
Land plants
ANCESTRAL
GREEN
ALGA
Nonvascular
plants
(bryophytes)
Liverworts
Characteristics of all land plants:
•
•
•
•
eukaryotic, multicellular, autotrophic
cell walls made mostly of cellulose
chlorophylls a & b
Domain Eukarya, Kingdom Plantae
In many plants, additional
terrestrial adaptations, such as
vascular tissues and secondary
compounds, also evolved.
Nonvascular plants
1. Represented by three phyla:
a. phylum Hepatophyta – liverworts
b. phylum Anthocerophyta – hornworts
c. phylum Bryophyta - mosses
Liverworts
Hornworts
Moss
Fig. 29-9a
Thallus
Gametophore of
female gametophyte
Sporophyte
Foot
Seta
Marchantia sporophyte (LM)
500 µm
Marchantia polymorpha,
a “thalloid” liverwort
Capsule
(sporangium)
2. The gametophyte is the dominant generation in
the life cycle
• gametophyte - mass of green, branched, one-cell-thick filaments
• sporophytes are smaller; only present part of the time
• spores germinate in favorable habitats
sporophyte
gametophyte
sporophyte
gametophyte
Raindrop
Fig. 29-8 The life cycle of a moss.
Sperm
“Bud”
Antheridia
Male
gametophyte
(n)
Key
Haploid (n)
Diploid (2n)
Protonemata
(n)
“Bud”
Egg
Spores
Gametophore
Female Archegonia
gametophyte (n)
Spore
dispersal
Rhizoid
Peristome
FERTILIZATION
Sporangium
MEIOSIS
Mature
sporophytes
Seta
Capsule
(sporangium)
Foot
(within archegonium)
Zygote
(2n)
Embryo
2 mm
Archegonium
Capsule with
peristome (SEM)
Young
sporophyte
(2n)
Female
gametophytes
3. Bryophyte sporophytes disperse enormous
numbers of spores
• sporophytes remain attached to gametophyte throughout the
lifetime
– depends on the gametophyte for sugars, amino acids, minerals and
water.
• sporangium (site of meiosis and spore production) can
generate over 50 million spores.
4. Bryophytes provide many ecological and
economic benefits
• distributed worldwide
• common and diverse in moist forests and wetlands
• Some common in extreme environments (mountaintops,
tundra, and deserts)
• Sphagnum, a wetland moss, is especially abundant and
widespread.
• forms extensive deposits of undecayed organic material,
called peat
• Wet regions dominated by Sphagnum or peat moss are known
as peat bogs
Fig. 29-11
(a) Peat being harvested
(b) “Tollund Man,” a bog mummy
Bog People
THE ORIGIN OF VASCULAR PLANTS
1. Two conducting tissues of the vascular system
A. Xylem –
Dead tissue, water-conducting
B. Phloem –
Living tissue, food-transporting
2. Water-conducting cells are strengthened by lignin and
provide structural support
3. Sporophyte generation is dominant in vascular plants.
Seedless vascular plants
4. Two modern phyla:
a. phylum Lycophyta – club mosses
b. phylum Pterophyta - ferns, whisk ferns, and horsetails
Club moss
Whisk fern
Horsetail
Fern
Fig. 29-15a
Lycophytes (Phylum Lycophyta)
2.5 cm
Isoetes
Strobili
(clusters of
gunnii,
a quillwort sporophylls)
1 cm
Selaginella apoda,
a spike moss
Diphasiastrum tristachyum, a club moss
Fig. 29-15e
Pterophytes (Phylum Pterophyta)
Athyrium
filix-femina,
lady fern
Equisetum
arvense,
field
horsetail
Psilotum
nudum,
a whisk
fern
Vegetative stem
2.5 cm
1.5 cm
25 cm
Strobilus on
fertile stem
5. Most seedless vascular plants are homosporous, producing
one type of spore that develops into a bisexual gametophyte
• both archegonia (female sex organs) and antheridia (male sex
organs)
• Eg., ferns
eggs
sporophyte
Single type
of spore
Bisexual
gametophyte
sperm
Fig. 29-13 The life cycle of a fern.
Key
Haploid (n)
Diploid (2n)
MEIOSIS
Spore
dispersal
Spore
(n)
Sporangium
Sporangium
Antheridium
Young
gametophyte
Mature
gametophyte
(n)
Archegonium
Egg
Mature
sporophyte
(2n)
New
sporophyte
Zygote
(2n)
Sorus
Gametophyte
Fiddlehead
FERTILIZATION
Sperm
6. seedless vascular plants are most common in damp habitats
7. ferns produce clusters of sporangia, called sori, on the back
of leaves
Seedless vascular plants formed vast “coal forests”
during the Carboniferous period
• These plants left not only living representatives
and fossils, but also fossil fuel in the form of coal.