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

2. Overview: The Greening of Earth
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
Plants supply oxygen and are the ultimate source of most food eaten by land animals

3. Overview: Multicellularity
Advantages
Multicellular organisms can be larger and operate more efficiently
Cells are specialized to perform specific functions which benefit the whole organism
Disadvantages
Multicellular organisms need to coordinate the activities of their individual cells
They are restricted in their exploitation of habitats because of their size.

4. How did plants change the world?
Fig. 29-1
How did plants change the world?
Figure 29.1 How did plants change the world?

5. Concept 29.1: Land plants (Kingdom Plantae) evolved from green algae!!!!!!
Green algae called charophytes are the closest relatives of land plants
Lower plants and green algae have flagellated sperm that is similar in structure
Homologous chloroplasts – chlorophyll b
Mitosis/cytokinesis – similarities
Genetic similarities in nuclear genes and rRNA
Food reserves - starch

6. Concept 29.1: Land plants (Kingdom Plantae) evolved from green algae!!!!!!
Multicellular, photosynthetic, and immobile, all plants have cellulose walls
Because most plants cannot move around, obtaining light for photosynthesis and bringing gametes together for sexual reproduction have been dominant themes in their evolution.
Plants originated in the sea, and some forms later colonized land. The most successful land plants have vascular tissues that transport food and water through the plant and support the body in the air.
Most successful vascular plants have adaptations freeing their reproduction from dependence on water. (cuticle, stomates, reduced gametophytes that are dependent on sporophytes)

7. Living on Land compared to Water
Advantages
More light
Higher concentration of CO2
Nutrients in soil
Disadvantages
no support for plant body
Less water available for reproduction
Segregated resources (light and air above, water and minerals below soil surface)
Extremes of temperature

8. Derived Traits of Plants
Four key traits appear in nearly all land plants but are absent in the charophytes:
Alternation of generations (with multicellular, dependent embryos)
Walled spores produced in sporangia
Multicellular gametangia
Apical meristems
Additional derived traits such as a cuticle and secondary compounds evolved in many plant species
Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients

9. Alternation of Generations and Multicellular, Dependent Embryos
Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations
The gametophyte is haploid and produces haploid gametes by mitosis
Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis. These spores germinate into gametophytes.
The gametophyte produces gametes by mitosis.
The gametes fuse for form a diploid zygote which grows into the sporophyte
In the evolutionary history of plants, the sporophyte generation has increased in size, number of cells and complexity while the gametophyte has decreased in size, number of cell and complexity. In higher plants, the sporophyte is the dominant form.

10. Alternation of generations
Fig. 29-5a
Gamete from
another plant
Gametophyte
(n)
Mitosis
Mitosis n n n n
Spore
Gamete
MEIOSIS
FERTILIZATION
Zygote 2n
Figure 29.5 Derived traits of land plants
Mitosis
Sporophyte
(2n)
Alternation of generations

11. Longitudinal section of Sphagnum sporangium (LM)
Fig. 29-5c
Spores (haploid)
Sporangium
Longitudinal section of
Sphagnum sporangium (LM)
Figure 29.5 Derived traits of land plants
Sporophyte (diploid) –
produces haploid spores
by meiosis
Gametophyte (haploid)
Sporophytes and sporangia of Sphagnum (a moss)

12. The Origin and Diversification of Plants
Those ancestral species gave rise to a vast diversity of modern plants
Land plants can be informally grouped based on the presence or absence of vascular tissue
Most plants have vascular tissue; these constitute the vascular plants
Nonvascular plants are commonly called bryophytes
Seedless vascular plants can be divided into clades
Lycophytes (club mosses and their relatives)
Pterophytes (ferns and their relatives)
A seed is an embryo and nutrients surrounded by a protective coat
Seed plants form a clade and can be divided into further clades:
Gymnosperms, the “naked seed” plants, including the conifers
Angiosperms, the flowering plants

13. Figure 29.7 Highlights of plant evolution1
Origin of land plants (about 475 mya) 2
Origin of vascular plants (about 420 mya) 3
Origin of extant seed plants (about 305 mya)
Liverworts
Nonvascular
plants
(bryophytes)
Land plants
ANCES-
TRAL
GREEN
ALGA 1
Hornworts
Mosses
Lycophytes (club mosses,
spike mosses, quillworts)
Seedless
vascular
plants 2
Vascular plants
Pterophytes (ferns,
horsetails, whisk ferns)
Figure 29.7 Highlights of plant evolution
Gymnosperms 3
Seed plants
Angiosperms
500
450
400
350
300 50
Millions of years ago (mya)

14. Concept 29.2: Mosses and other nonvascular plants have life cycles dominated by gametophytes
Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants:
Liverworts, phylum Hepatophyta
Hornworts, phylum Anthocerophyta
Mosses, phylum Bryophyta
Mosses are most closely related to vascular plants
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms

15. Bryophytes - Mosses and other nonvascular plants have life cycles dominated by gametophytes
The hapliod gametophyte is the dominant generation
The sporphyte is dependent on the gametopyhte
Must have water
to reproduce so that the sperm can swim to the egg
because no vascular tissue to carry water to plants parts, therefore, plants are always low to the ground
Bryophyte sporophytes grow out of archegonia, and are the smallest and simplest sporophytes of all extant plant groups.
Although bryophyte sporophytes are usually green and photosynthetic when young, they cannot live independently. They remain attached to their parental gametophytes, from which they absorb sugars, amino acids, minerals, and water.

16. Figure 29.8 The life cycle of a moss
Raindrop
Sperm
“Bud”
Antheridia
Male
gametophyte
(n)
Key
Haploid (n)
Protonemata
(n)
Diploid (2n)
“Bud”
Egg
Spores
Gametophore
Archegonia
Spore
dispersal
Female
gametophyte (n)
Rhizoid
Peristome
Sporangium
FERTILIZATION
Figure 29.8 The life cycle of a moss
MEIOSIS
(within archegonium)
Seta
Zygote
(2n)
Capsule
(sporangium)
Mature
sporophytes
Foot
Embryo
Archegonium
Young
sporophyte
(2n)
2 mm
Capsule with
peristome (SEM)
Female
gametophytes

17. Life Cycle of Mosses - Animation

18. Polytrichum commune, hairy-cap moss Sporophyte (a sturdy Capsule
Fig. 29-9d
Polytrichum commune,
hairy-cap moss
Sporophyte
(a sturdy
plant that
takes months
to grow)
Capsule
Seta
Figure 29.9 Bryophyte diversity
Gametophyte

19. The Ecological and Economic Importance of Mosses
Moses are capable of inhabiting diverse and sometimes extreme environments, but are especially common in moist forests and wetlands
Some mosses might help retain nitrogen in the soil
Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat – peat has long been a fuel source in Europe and Asia
Sphagnum is an important global reservoir of organic carbon (good CO2 sink)

20. Annual nitrogen loss (kg/ha)
Fig
RESULTS 6 5 4
Annual nitrogen loss
(kg/ha) 3 2
Figure Can bryophytes reduce the rate at which key nutrients are lost from soils? 1
With moss
Without moss

21. (a) Peat being harvested
Fig
(a) Peat being harvested
Figure Sphagnum, or peat moss: a bryophyte with economic, ecological, and archaeological significance
(b) “Tollund Man,” a bog mummy – acidic, oxygen-poor conditions preserve organisms

22. Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall
Vascular tissue allowed these plants to grow tall
Seedless vascular plants have flagellated sperm and are usually restricted to moist environments
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms

23. Origins and Traits of Vascular Plants (xylem & phloem tissue)
Living vascular plants are characterized by:
Life cycles with dominant sporophytes, however, the gametophytes are photosynthetic and are not dependent on the sporophyte for nutrition.
The gametophytes are tiny plants that grow on or below the soil surface
Have roots that take up water from the soil and vascular tissue that transports it to leaves and stems up in the sunlight
Must live in somewhat moist areas because their sexual reproduction still depends on water for flagellated sperm to swim in.

24. Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte
Fig
Key
Haploid (n)
Diploid (2n)
Spore
(n)
Antheridium
Young
gametophyte
Spore
dispersal
MEIOSIS
Sporangium
Mature
gametophyte
(n)
Sperm
Archegonium
Egg
Mature
sporophyte
(2n)
Sporangium
New
sporophyte
Zygote
(2n)
FERTILIZATION
Sorus
Figure The life cycle of a fern
Gametophyte
Fiddlehead

25. Transport in Xylem and Phloem
Vascular plants have two types of vascular tissue: xylem and phloem
Xylem conducts most of the water and minerals and includes dead cells called tracheids
Phloem consists of living cells and distributes sugars, amino acids, and other organic products
Water-conducting cells are strengthened by lignin and provide structural support
Increased height was an evolutionary advantage

26. Evolution of Roots Evolution of Leaves
Roots are organs that anchor vascular plants
They enable vascular plants to absorb water and nutrients from the soil
Roots may have evolved from subterranean stems
Evolution of Leaves
Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

27. Athyrium filix-femina, lady fern 25 cm Fig. 29-15f
Figure Seedless vascular plant diversity
25 cm

28. The Significance of Seedless Vascular Plants
The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Devonian and Carboniferous, forming the first forests
Photosynthesis dramatically increased the removal of CO2 from the atmosphere
Increased photosynthesis may have helped produce the global cooling at the end of the Carboniferous period
The decaying plants of these Carboniferous forests eventually became coal
Coal was crucial to the Industrial Revolution, and people worldwide still burn 6 billion tons a year.
Ironic that coal, formed from plants that contributed to global cooling, now contributes to global warming by returning carbon to the atmosphere.

29. Fig
Figure Artist’s conception of a Carboniferous forest based on fossil evidence

30. You should now be able to:
Describe four shared characteristics and four distinct characteristics between green algae and land plants
Explain why most bryophytes grow close to the ground and are restricted to periodically moist environments
Describe three traits that characterize modern vascular plants and explain how these traits have contributed to success on land
Explain how vascular plants differ from bryophytes