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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
An Overview of Land Plant Evolution
• 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
• Land plants evolved from green algae
(chlorophyta):
– Researchers have identified green algae called
charophyceans as the closest relatives of land
plants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Evolution of Plants
• The first plants evolved from an organism much like the
multicellular green algae living today
–
However, the evolution of plants favored species that were more
resistant to the drying rays of the sun!
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview of Land Plant Evolution
• > 280,000 species of plants inhibit Earth today.
• 4 major evolutionary trends characterize plants
today:
– Movement to land (new niches)
– Development of vascular tissue (taller growth)
– Development of seeds (dispersal of offspring)
– Development of flowers (pollinators)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 29.1 Some highlights of plant evolution
Morphological and Biochemical Evidence
• Land plants evolved from charophycean algae over 500
million years ago. There are four key traits that land plants
share only with charophyceans:
–
Rose-shaped complexes for cellulose synthesis
•
–
Peroxisome enzymes
•
–
Help minimize the loss of organic product due to photorespiration
Structure of flagellated sperm
•
–
Rose-shaped array of proteins that synthesize the cellulose
microfibrils of the cell wall
Used for sperm motility
Formation of a phragmoplast
•
An alignment of cytoskeletal elements and Golgi-derived vesicles
across the midline of the dividing cell.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Derived Traits of Plants
• Five key traits appear in nearly all land plants
but are absent in the charophyceans:
– Apical meristems
– Multicellular dependent embryos
– Alternation of generations
– Walled spores produced in sporangia
– Multicellular gametangia
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Apical Meristems – Producers of Plant’s Tissues
• These are localized regions of cell division at the tips
of shoots and roots.
– Maximize their exposure to environmental resources.
Developing
leaves
Apical
meristem
of shoot
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Apical
meristem
of root
Multicellular Dependent Embryos
• Multicellular plant embryos develop from
zygotes that are retained within tissues of the
female parent.
– Parental tissues provide developing embryo
with nutrients.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Alternation of Generations Life Cycle
• During the life cycle of ALL land plants, two
multicellular body forms alternate, each form producing
the other.
– Called alternation of generations
– Cells of gametophyte generation are haploid (single
set of chromosomes) – produces gametes
• Fusion of gametes (eggs and sperm) during
fertilization forms diploid zygotes.
– Mitotic division of the zygote produces the multicellular
sporophyte (diploid).
• Meiosis in a mature sporophyte produces haploid
reproductive cells called spores (reproductive cells
that can develop into a new organism without fusing
with another cell). Mitotic division of spore
produces new gametophyte…so cycle continues.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 29.6 Alternation of generations: a generalized scheme
Walled Spores Produced in Sporangia
• Plant spores are haploid reproductive cells that have the
potential to grow into multicellular, haploid gametophytes
by mitosis.
–
A polymer called sporopollenin (durable organic material) makes walls
of plant spores tough and resistant to harsh environments.
–
Multicellular organs called sporangia, found on the sporophyte generation
of a plant, produce the spores.
–
The outer tissues of the sporangium protect developing spores until they
are ready to be released – a key adaptation in land plants.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Multicellular Gametangia
• The gametophyte forms of bryophytes, pteridophytes, and
gymnosperms all produce their gametes within multicellular
organs called gametangia.
–
Female gametangia are called archegonia
–
Male gametangia are called antheridia
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Other Terrestrial Adaptations Common to Land Plants
• Adaptations for water conservation
– Cuticle (waxy cover on surface of stems and leaves)
– Stomata (pore on leaves allowing for gas exchange)
• Adaptations for Water Transport
– Xylem (carries water and minerals from roots to rest of
plant)
– Phloem (carries sugars and other nutrients throughout
plant)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4 Main Groups of Land Plants
• Bryophytes: non-vascular plants
– mosses, hornworts, and liverworts
• Pteridophytes: seedless vascular plants
– Club moss, horsetails, ferns
• Gymnosperms: vascular seeded cone-bearers
– Ginkgos, cycads, gnetophytes, conifers
• Angiosperms: vascular seeded flowering plants
– Monocots & dicots
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 22-7 The Diversity of Plants
22-1
LandSection
plants
can be informally grouped based on the presence or
absence of vascular tissue
Cone-bearing plants
760 species
Ferns and
their relatives
11,000 species
Mosses and
their relatives
15,600 species
Go to
Section:
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Flowering
plants
235,000 species
Table 29.1 Ten Phyla of Extant Plants
An Overview of Land Plant Evolution
Land plants
Vascular plants
Figure 29.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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 – Nonvascular Plants
• 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
• In all three bryophyte phyla
–
Gametophytes are larger and longer-living than sporophytes
–
Water is required for survival AND reproduction – absorb water by diffusion
–
Have no true roots, stems, and leaves and lack lignin-fortified tissue required to
support tall plants on land
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Life Cycle of Moss
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Tracheophytes – Vascular Plants
• Most common and widespread of land plants
• Have true vascular tissues -- xylem and phloem that
allow true “organs” to develop – roots, stems, leaves
– Xylem carries water and minerals in a plant
– Phloem carries nutrients in a plant
• Two categories
– Seedless (reproduce by spores)
– Seeded (reproduce by seeds)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Life Cycles with Dominant Sporophytes
• In contrast with bryophytes
– The 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
• All seed plants and some seedless vascular
plants are heterosporous, having two types of
spores that give rise to male and female
gametophytes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Figure 29.24b Fern sporophyll, a leaf specialized for spore production
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
• Since they don’t have seeds, they need LOTS of
water for fertilization
– USE SPORES TO REPRODUCE FOR MAJORITY OF
LIFE; gametes are used only for a short period of time
• Display alternation of generations – part of time is
asexual (uses spores), part is sexual (uses gametes)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Figure 29.21 Pteridophytes: club "moss" (top left), whisk fern (top right), horsetail
(bottom left), fern (bottom right)
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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 Significance 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Evolution of Plants
Vascular w/ Seeds
Vascular w/ Seeds
Angiosperms
Vascular Seedless Gymnosperms
Non-Vascular
Pterophyta
Flowering
plants
Bryophytes
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor