Download Origins and Traits of Vascular Plants

Chapter 29
Plant Diversity I
How Plants
Colonized Land
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
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• 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
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• 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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• Concept 29.1: Land plants evolved from green
algae
• Researchers have identified green algae called
charophyceans as the closest relatives of land
plants
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Morphological and Biochemical Evidence
• Many characteristics of land plants
– Also appear in a variety of algal clades
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• There are four key traits that land plants share
only with charophyceans
– Rose-shaped complexes for cellulose
synthesis
Figure 29.2
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30 nm
– Peroxisome enzymes
– Structure of flagellated sperm
– Formation of a phragmoplast
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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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• Concept 29.2: Land plants possess a set of
derived terrestrial adaptations (Allowed plants
from drying out)– begin by being close to lakes
and ponds.
• Many adaptations
– Emerged after land plants diverged from their
charophycean relatives
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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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• Some biologists think that the plant kingdom
– Should be expanded to include some or all
green algae
• Until this debate is resolved
– This textbook retains the embryophyte
definition of kingdom Plantae
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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
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• 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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• 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
• Additional derived units
– Such as a cuticle and secondary compounds,
evolved in many plant species
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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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• Fossilized spores and tissues
– Have been extracted from 475-million-year-old
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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• 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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Characteristics of Plant Phylums
General characteristics
Bryophytes
Nonvascular Plant (No extensive transport
system)
Shared derived traits from the vascular plants
which include the apical meristem and cellular
embryos.
Lack roots and stems
Seedless Vascular Plants
Lycophytes
Pterophytes
Seedless Vascular Plants (closer to the vascular
plants on a cladogram)
Examples
Liverworts, Hornworts,
and mosses
Lycophytes: Club moss,
spike moss, and
quillworts
Pterophytes: Ferns,
horsetails, and whisk
ferns
Gymnosperms
Cone bearing
Naked seeds
Needlelike leaves
Angiosperms
Flowering plants
All flowering plants
Seeds enclosed in an ovary which mature into fruit (Maples, Oaks, Tulips,
Grasses, Beans)
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Ginkgo Cycads
Gnetophytes, and
Coniferes
• Land plants can be informally grouped
– Based on the presence or absence of vascular
tissue
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• 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)
• Concept 29.3: 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
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• Debate continues over the sequence of
bryophyte evolution
• Mosses are most closely related to vascular
plants
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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
Raindrop
1 Spores develop into
threadlike protonemata.
Key
Male
gametophyte
Haploid (n)
Diploid (2n)
Sperm
“Bud”
2 The haploid
protonemata
produce “buds”
that grow into
gametophytes.
Protonemata
4 A sperm swims
through a film of
moisture to an
archegonium and
fertilizes the egg.
Antheridia
3 Most mosses have separate
male and female gametophytes,
with antheridia and archegonia,
respectively.
“Bud”
Egg
Spores
Gametophore
Female
Archegonia
spores develop in the sporangium gametophyte
of the sporophyte. When the
Rhizoid
sporangium lid pops off, the
peristome “teeth” regulate
6 The sporophyte grows a
gradual release of the spores. long stalk, or seta, that emerges
Seta
from the archegonium.
8 Meiosis occurs and haploid
Peristome
Sporangium
MEIOSIS
Mature
Mature
sporophytes
sporophytes
Capsule
(sporangium)
FERTILIZATION
(within archegonium)
Calyptra
Zygote
Embryo
Foot
Archegonium
Young
sporophyte
Capsule with
peristome (LM)
Figure 29.8
Female
gametophytes
5 The diploid zygote
develops into a
sporophyte embryo within
Attached
by
its
foot,
the
7
the archegonium.
sporophyte remains nutritionally
dependent on the gametophyte.
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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
• 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
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
• 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
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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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• 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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• The life cycle of a fern
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 and phloem
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• 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
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• Leaves are categorized by two types
– Microphylls, leaves with a single vein
– Megaphylls, leaves with a highly branched
vascular system
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• 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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• 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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• The general groups of 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 Lycophyta: Club Mosses, Spike Mosses, and
Quillworts
• Modern species of lycophytes
– Are relics from a far more eminent past
– Are small herbaceous plants
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Phylum Pterophyta: Ferns, Horsetails, and Whisk
Ferns and Relatives
• 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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• 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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