1. Plant Diversity I How Plants Colonized Land
Chapter 29
Plant Diversity I How Plants Colonized Land

2. Overview: The Greening of Earth Looking at a lush landscape
It is difficult to imagine the land without any plants or other organisms
Figure 29.1

3. For more than the first 3 billion years of Earth’s history
The terrestrial surface was lifeless
Since colonizing land
Plants have diversified into roughly 290,000 living species

4. Concept 29.1: Land plants evolved from green algae
Researchers have identified green algae called charophyceans as the closest relatives of land plants

5. Morphological and Biochemical Evidence
Many characteristics of land plants
Also appear in a variety of algal clades

6. There are four key traits that land plants share only with charophyceans
Rose-shaped complexes for cellulose synthesis
30 nm
Figure 29.2

7. Peroxisome enzymes
Structure of flagellated sperm
Formation of a phragmoplast

8. Concept 29.2: Land plants possess a set of derived terrestrial adaptations
Many adaptations
Emerged after land plants diverged from their charophycean relatives

9. Derived Traits of Plants
Five key traits appear in nearly all land plants but are absent in the charophyceans
Apical meristems
Alternation of generations
Walled spores produced in sporangia
Multicellular gametangia
Multicellular dependent embryos

10. Apical meristems and alternation of generations
of shoot
Developing
leaves
100 µm
Apical meristems of plant shoots
and roots. The light micrographs
are longitudinal sections at the tips
of a shoot and root.
Apical meristem
of root
Root
Shoot
Figure 29.5
Haploid multicellular
organism (gametophyte)
Mitosis
Gametes
Zygote
Diploid multicellular
organism (sporophyte)
Alternation of generations: a generalized scheme
MEIOSIS
FERTILIZATION 2n n
Spores
ALTERNATION OF GENERATIONS
Figure 29.5

11. Walled spores; multicellular gametangia; and multicellular, dependent embryos
WALLED SPORES PRODUCED IN SPORANGIA
Sporangium
Sporophyte and sporangium of Sphagnum (a moss)
Longitudinal section of
Sphagnum sporangium (LM)
Sporophyte
Gametophyte
MULTICELLULAR GAMETANGIA
Female gametophyte
Archegonium
with egg
Archegonia and antheridia of Marchantia (a liverwort)
Antheridium
with sperm
Male
gametophyte
MULTICELLULAR, DEPENDENT EMBRYOS
Embryo
Maternal tissue
2 µm
Embryo and placental transfer cell of Marchantia
10 µm
Figure 29.5
Wall ingrowths
Placental transfer cell

12. The Origin and Diversification of Plants
Fossil evidence
Indicates that plants were on land at least 475 million years ago

13. Fossilized spores and tissues
Have been extracted from 475-million-year-old rocks
Fossilized spores.
Unlike the spores of
most living plants,
which are single
grains, these spores
found in Oman are
in groups of four
(left; one hidden)
and two (right).
(a)
Fossilized
sporophyte tissue.
The spores were
embedded in tissue
that appears to be
from plants.
(b)
Figure 29.6 a, b

14. Land plants can be informally grouped
Based on the presence or absence of vascular tissue

15. Debate continues over the sequence of bryophyte evolution
Mosses are most closely related to vascular plants

16. Ecological and Economic Importance of Mosses
Sphagnum, or “peat moss”
Forms extensive deposits of partially decayed organic material known as peat
Plays an important role in the Earth’s carbon cycle
(a)
Peat being harvested from a peat bog
Sporangium at
tip of sporophyte
Gametophyte
(b)
Closeup of Sphagnum. Note the “leafy” gametophytes
and their offspring, the sporophytes.
Living
photo-
synthetic
cells
Dead water-
storing cells
100 µm
(c)
Sphagnum “leaf” (LM). The combination of living photosynthetic
cells and dead water-storing cells gives the moss its spongy quality.
(d)
“Tolland Man,” a bog mummy dating from 405–100 B.C.
The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years.
Figure a–d

17. Bryophytes and bryophyte-like plants
Concept 29.4: Ferns and other seedless vascular plants formed the first forests
Bryophytes and bryophyte-like plants
Were the prevalent vegetation during the first 100 million years of plant evolution
Vascular plants
Began to evolve during the Carboniferous period

18. Transport in Xylem and Phloem
Vascular plants have two types of vascular tissue
Xylem and phloem

19. Xylem Phloem Conducts most of the water and minerals
Includes dead cells called tracheids
Phloem
Distributes sugars, amino acids, and other organic products
Consists of living cells

20. Evolution of Roots Roots Are organs that anchor vascular plants
Enable vascular plants to absorb water and nutrients from the soil
May have evolved from subterranean stems

21. Evolution of Leaves Leaves
Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis

22. Leaves are categorized by two types
Microphylls, leaves with a single vein
Megaphylls, leaves with a highly branched vascular system

23. Sporophylls and Spore Variations
Are modified leaves with sporangia
Most seedless vascular plants
Are homosporous, producing one type of spore that develops into a bisexual gametophyte

24. All seed plants and some seedless vascular plants
Are heterosporous, having two types of spores that give rise to male and female gametophytes

25. Classification of Seedless Vascular Plants
Seedless vascular plants form two phyla
Lycophyta, including club mosses, spike mosses, and quillworts
Pterophyta, including ferns, horsetails, and whisk ferns and their relatives

26. The general groups of seedless vascular plants
LYCOPHYTES (PHYLUM LYCOPHYTA)
PTEROPHYTES (PHYLUM PTEROPHYTA)
WHISK FERNS AND RELATIVES
HORSETAILS
FERNS
Isoetes
gunnii,
a quillwort
Selaginella apoda,
a spike moss
Diphasiastrum tristachyum, a club moss
Strobili
(clusters of
sporophylls)
Psilotum
nudum,
a whisk
fern
Equisetum
arvense,
field
horsetail
Vegetative stem
Strobilus on
fertile stem
Athyrium
filix-femina,
lady fern
Figure 29.14

27. Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives
Are the most diverse seedless vascular plants

28. The growth of these early forests
May have helped produce the major global cooling that characterized the end of the Carboniferous period
Decayed and eventually became coal

29. The End