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Chapter 29
Plant Diversity I
How Plants
Colonized Land
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Early life
• 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
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Plant evolution
• Land plants evolved from green algae
• Researchers have identified green algae
called charophyceans as the closest
relatives of land plants
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Evolution of Plants
• There are four key traits that land plants share only
with charophyceans
– Rose-shaped complexes for cellulose synthesis
– Peroxisome enzymes
– Structure of flagellated sperm
– Formation of a phragmoplast
(Alignment of cytoskeleton
and golgi vesicles across the midline of the dividing cell)
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Figure 29.2
30 nm
Genetic Evidence
• Comparisons of both nuclear and chloroplast
genes
– Point to charophyceans as the closest living
relatives of land plants
(a) Chara,
a pond
organism
10 mm
40 µm
Figure 29.3a, b
(b) Coleochaete orbicularis, a diskshaped charophycean (LM)
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Adaptations Enabling the Move to Land
• In charophyceans
– A layer of a durable polymer called
sporopollenin prevents exposed zygotes
from drying out
• The accumulation of traits that facilitated
survival on land
– May have opened the way to its colonization
by plants
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Defining the Plant Kingdom
• Systematists
– Are currently debating the boundaries of
the plant kingdom
Viridiplantae
Streptophyta
Plantae
Red algae
Figure 29.4
Chlorophytes Charophyceans Embryophytes
Ancestral alga
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Derived Traits of Plants
• Five derived 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
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Derived Characters of Plants
• Apical meristems and alternation of
generations
APICAL MERISTEMS
Apical
meristem
of shoot
Developing
leaves
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
Shoot
Root
100 µm
100 µm
Haploid multicellular
organism (gametophyte)
Mitosis
Mitosis
n
n
n
ALTERNATION OF GENERATIONS
Spores
n
n
Gametes
MEIOSIS
FERTILIZATION
2n
Figure 29.5
2n
Zygote
Mitosis
Diploid multicellular
organism (sporophyte)
Alternation of generations: a generalized scheme
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Derived Characters of Plants
• Walled spores; multicellular gametangia; and
multicellular, dependent embryos
WALLED SPORES PRODUCED IN SPORANGIA
Spores
Sporangium
Sporophyte and sporangium
of Sphagnum (a moss)
Longitudinal section of
Sphagnum sporangium (LM)
Sporophyte
Gametophyte
MULTICELLULAR GAMETANGIA
Female gametophyte
Archegonium
with egg
Antheridium
with sperm
Archegonia and antheridia
of Marchantia (a liverwort)
Male
gametophyte
MULTICELLULAR, DEPENDENT EMBRYOS
Embryo and placental
transfer cell of Marchantia
Figure 29.5
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Embryo
Maternal tissue
2 µm
10 µm
Wall ingrowths
Placental transfer cell
Derived Characters of Plants
• Additional derived units
– Such as a cuticle and secondary compounds,
evolved in many plant species
2° Compounds
Alkaloids
Terpenes
Tannins
Phenolics
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The Origin and Diversification of Plants
• Fossil evidence
– Indicates that plants were on land at least
475 million years ago
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Origin of Plants
• Fossilized spores and tissues
– Have been extracted from 475-million-yearold rocks
(a) 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).
(b) Fossilized
Figure 29.6 a, b
sporophyte tissue.
The spores were
embedded in tissue
that appears to be
from plants.
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Diversity of Plants
• Whatever the age of the first land plants
– Those ancestral species gave rise to a vast
diversity of modern plants
Table 29.1
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Plant Classification
• Land plants can be informally grouped
– Based on the presence or absence of
vascular tissue
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Plant Evolution
• An overview of land plant evolution
Land plants
Vascular plants
Figure 29.7
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Angiosperms
Origin of seed plants
(about 360 mya)
Origin of vascular
plants (about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
Seed plants
Gymnosperms
Pterophyte
(ferns, horsetails, whisk fern)
Seedless vascular plants
Lycophytes
(club mosses, spike mosses, quillworts)
Mosses
Hornworts
Liverworts
Charophyceans
Bryophytes
(nonvascular plants)
Bryophytes
• The life cycles of mosses and other bryophytes are
dominated by the gametophyte stage
• Bryophytes are represented today by three phyla of
small herbaceous (nonwoody) plants
– Liverworts, phylum Hepatophyta
– Hornworts, phylum Anthocerophyta
– Mosses, phylum Bryophyta
**Debate continues over the sequence of bryophyte evolution
Mosses are most closely related to vascular plants
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Non Vascular Plants
• Liverworts
• - Grow horizontally due to the lack of vascular tissue
• - Rhizoids “Root like, but w/o conducting cells
• - Gametophyte is dominant form “Thallus form”
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Non Vascular Plants
• Hornworts
• - Grow low to ground due to lack of vascular tissue
• - Gametophyte is dominant form
• - Have rhizoids
• - Grow in damp humid places
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Non Vascular Plants
• Mosses
• - Gametophyte grows vertically (Unlike liverworts &
hornworts)
• - Gametophyte is dominant form
• - Prefer a damp shady environment
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Bryophyte Gametophytes
• In all three bryophyte phyla
– Gametophytes are larger and longer-living
than sporophytes
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The life cycle of a moss
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Bryophyte Gametophytes
– Produce flagellated sperm in antheridia
– Produce ova in archegonia
– Generally form ground-hugging carpets and are at
most only a few cells thick
• Some mosses
– Have conducting tissues in the center of their
“stems” and may grow vertically
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Bryophyte Sporophytes
– Grow out of archegonia
– Are the smallest and simplest of all extant plant
groups
– Consist of a foot, a seta, and a sporangium
• Hornwort and moss sporophytes
– Have stomata
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Bryophyte Diversity Review
Gametophore of
female gametophyte
LIVERWORTS (PHYLUM HEPATOPHYTA)
Plagiochila
deltoidea,
a “leafy”
liverwort
Foot
Seta
Marchantia sporophyte (LM)
HORNWORTS (PHYLUM ANTHOCEROPHYTA)
An Anthoceros
hornwort species
Sporophyte
Sporangium
500 µm
Marchantia polymorpha,
a “thalloid” liverwort
MOSSES (PHYLUM BRYOPHYTA)
Polytrichum commune,
hairy-cap moss
Sporophyte
Gametophyte
Gametophyte
Figure 29.9
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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
(b) Closeup of Sphagnum. Note the “leafy” gametophytes
and their offspring, the sporophytes.
Gametophyte
(c) Sphagnum “leaf” (LM). The combination of living photosynthetic
cells and dead water-storing cells gives the moss its spongy quality.
Figure 29.10 a–d
(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.
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Sporangium at
tip of sporophyte
Living
photo- Dead watersynthetic storing cells
100 µm
cells
Seedless Vascular Plants
• 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
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Origins and Traits of Vascular Plants
• Fossils of the forerunners of vascular plants
– Date back about 420 million years
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Vascular Plants
• These early tiny plants
– Had independent, branching sporophytes
– Lacked other derived traits of vascular plants
Figure 29.11
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Life Cycles with Dominant Sporophytes
• In contrast with bryophytes
– Sporophytes of seedless vascular plants are the
larger generation, as in the familiar leafy fern
– The gametophytes are tiny plants that grow on or
below the soil surface
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Fern Life Cycle
1 Sporangia release spores.
Most fern species produce a single
type of spore that gives rise to a
bisexual gametophyte.
Key
2 The fern spore
develops into a small,
photosynthetic gametophyte.
3 Although this illustration
shows an egg and sperm
from the same gametophyte,
a variety of mechanisms
promote cross-fertilization
between gametophytes.
Haploid (n)
Diploid (2n)
Antheridium
Spore
MEIOSIS
Young
gametophyte
Sporangium
Archegonium
Mature
sporophyte
New
sporophyte
Sperm
Egg
Zygote
Sporangium
FERTILIZATION
Sorus
6 On the underside
of the sporophyte‘s
reproductive leaves
are spots called sori.
Each sorus is a
cluster of sporangia.
Gametophyte
Fiddlehead
Figure 29.12
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5 A zygote develops into a new
sporophyte, and the young plant
grows out from an archegonium
of its parent, the gametophyte.
4 Fern sperm use flagella
to swim from the antheridia
to eggs in the archegonia.
Transport in Xylem and Phloem
• Vascular plants have two types of vascular tissue
Xylem - 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
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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
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Evolution of Leaves
• Leaves
– Are organs that increase the surface area of
vascular plants, thereby capturing more solar
energy for photosynthesis
Leaves are categorized by two types
Microphylls, leaves with a single vein
Megaphylls, leaves with a highly branched
vascular system
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Evolution of Leaves
• According to one model of evolution
– Microphylls evolved first, as outgrowths of stems
Vascular tissue
Figure 29.13a, b
(a) Microphylls, such as those of lycophytes, may have
originated as small stem outgrowths supported by
single, unbranched strands of vascular tissue.
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(b) Megaphylls, which have branched vascular
systems, may have evolved by the fusion of
branched stems.
Sporophylls and Spore Variations
• Sporophylls
– Are modified leaves with sporangia
• Most seedless vascular plants
– Are homosporous, producing one type of spore that
develops into a bisexual gametophyte
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Heterospory
• All seed plants and some seedless vascular plants
– Are heterosporous, having two types of spores that
give rise to male and female gametophytes
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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
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Seedless Vascular Plants
LYCOPHYTES (PHYLUM LYCOPHYTA)
Strobili
(clusters of
sporophylls)
Isoetes
gunnii,
a quillwort
Selaginella apoda,
a spike moss
Diphasiastrum tristachyum, a club moss
PTEROPHYTES (PHYLUM PTEROPHYTA)
Psilotum
nudum,
a whisk
fern
Equisetum
arvense,
field
horsetail
Athyrium
filix-femina,
lady fern
Vegetative stem
Strobilus on
fertile stem
Figure 29.14
WHISK FERNS AND RELATIVES
HORSETAILS
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FERNS
Phylum Pterophyta
Ferns
Horsetails
Whisk Ferns
• Ferns
– Are the most diverse seedless vascular plants
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The Significance of Seedless Vascular Plants
• The ancestors of modern lycophytes, horsetails, and ferns
– Grew to great heights during the Carboniferous,
forming the first forests
Figure 29.15
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Importance of Seedless Vascular Plants
• 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
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