Chapter 29 Plant Diversity I How Plants Colonized Land

1
Chapter 29
Plant Diversity I How Plants Colonized Land
2
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

3

• 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

4
Fig. 29-5e
Apical meristems
Developing leaves
Apical meristem of shoot
Apical meristem of root
Shoot
Root
100 µm
100 µm
5
Fig. 29-5b
Embryo
2 µm
Maternal tissue
Wall ingrowths
10 µm
Placental transfer cell (outlined in blue)
Embryo (LM) and placental transfer cell (TEM) of
Marchantia (a liverwort)
6
Fig. 29-5a
Gamete from another plant
Gametophyte (n)
Mitosis
Mitosis
n
n
n
n
Spore
Gamete
FERTILIZATION
MEIOSIS
Zygote
2n
Mitosis
Sporophyte (2n)
Alternation of generations
7
Fig. 29-5c
Spores
Sporangium
Longitudinal section of Sphagnum sporangium (LM)
Sporophyte
Gametophyte
Sporophytes and sporangia of Sphagnum (a moss)
8
Fig. 29-5d
Archegonium with egg
Female gametophyte
Antheridium with sperm
Male gametophyte
Archegonia and antheridia of Marchantia (a
liverwort)
9
Fig. 29-7
Origin of land plants (about 475 mya)
1
Origin of vascular plants (about 420 mya)
2
3
Origin of extant seed plants (about 305 mya)
Liverworts
Nonvascular plants (bryophytes)
Land plants
Hornworts
1
ANCES- TRAL GREEN ALGA
Mosses
Lycophytes (club mosses, spike mosses, quillworts)
Seedless vascular plants
Vascular plants
2
Pterophytes (ferns, horsetails, whisk ferns)
Gymnosperms
3
Seed plants
Angiosperms
500
450
400
50
0
350
300
Millions of years ago (mya)
10
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.

11
Nonvascular plants

• 1. Represented by three phyla
• a. phylum Hepatophyta liverworts
• b. phylum Anthocerophyta hornworts
• c. phylum Bryophyta - mosses

Liverworts
Hornworts
Moss
12
Fig. 29-9a
Gametophore of female gametophyte
Thallus
Sporophyte
Foot
Seta
Capsule (sporangium)
Marchantia polymorpha, a thalloid liverwort
500 µm
Marchantia sporophyte (LM)
13

• 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
sporophyte
gametophyte
gametophyte
14
Fig. 29-8 The life cycle of a moss.
Raindrop
Sperm
Bud
Antheridia
Male gametophyte (n)
Key
Haploid (n)
Protonemata (n)
Diploid (2n)
Bud
Egg
Gametophore
Spores
Archegonia
Female gametophyte (n)
Spore dispersal
Rhizoid
Peristome
FERTILIZATION
Sporangium
(within archegonium)
MEIOSIS
Seta
Zygote (2n)
Capsule (sporangium)
Mature sporophytes
Foot
Embryo
Archegonium
Young sporophyte (2n)
2 mm
Female gametophytes
Capsule with peristome (SEM)
15

• 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.

16

• 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)

17

• 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

18
Fig. 29-11
(a) Peat being harvested
(b) Tollund Man, a bog mummy
19
Bog People
20
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.

21
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
22
Fig. 29-15a
Lycophytes (Phylum Lycophyta)
2.5 cm
Isoetes gunnii, a quillwort
Strobili (clusters of sporophylls)
Selaginella apoda, a spike moss
1 cm
Diphasiastrum tristachyum, a club moss
23
Fig. 29-15e
Pterophytes (Phylum Pterophyta)
Athyrium filix-femina, lady fern
Psilotum nudum, a whisk fern
Equisetum arvense, field horsetail
Vegetative stem
Strobilus on fertile stem
25 cm
1.5 cm
2.5 cm
24

• 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
Single type of spore
Bisexual gametophyte
sporophyte
sperm
25
Fig. 29-13 The life cycle of a fern.
Key
Haploid (n)
Diploid (2n)
Antheridium
Spore (n)
Young gametophyte
Spore dispersal
MEIOSIS
Sporangium
Mature gametophyte (n)
Sperm
Archegonium
Egg
Mature sporophyte (2n)
New sporophyte
Sporangium
Zygote (2n)
FERTILIZATION
Sorus
Gametophyte
Fiddlehead
26

• 6. seedless vascular plants are most common in
  damp habitats
• 7. ferns produce clusters of sporangia, called
  sori, on the back of leaves

27
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.