Chapter 29: Overview of Plant
Diversity
Divya Raj, Katie Redinger, Allie
Wrabel
The Evolutionary Origins of Plants
• Plant will refer to a group of organisms that
share a freshwater algal ancestor and have
evolved over a 470-million-year period
• The exact ancentral alga is still a mystery, but
close relatives like the Charales exist today
• The shared history green algae has with other
plants has led scientists to change the name of
kingdom Plante to kingdom Viridiplante to
include the algae
Land Plants
• All afford protection to
their embryos
• All have multicellular
haploid and diploid
phases
Conductive Systems
• Nonvascular Plants- lack vascular tissue
• Vascular Plants- have water-conduction
xylem and food-conducting phloem
strands of tissues in their stems, roots,
and leaves.
Four Major Groups of Land Plants
• Nonvascular plants- not monophyletic, include
three phyla: mosses, liverworts, and hornworts
• Seedless vascular plants- (1) club mosses, and
(2) ferns, whisk ferns, and horsetails.
• Gymnosperms- have seeds that protect their
embryos
• Angiosperms- have flowers, which may attract
pollinators, and fruits surrounding the seeds,
protecting the embryos and aiding in seed
dispersal
Adaptations to Land
• Many plants are protected from
desiccation-the tendency of organisms to
lose water to the air-by a cuticle that is
secreted onto their exposed surfaces
• Gas diffusion into and out of the plant
occurs though tiny openings called
stomata
• Evolution of leaves increases the amount
of photosynthetic surface area
Plant Life Cycles
• Humans have diplontic life cycles, while
plants have haplodiplontic
• Diploid sporophytes produce haploid
spores by meiosis
• Spores develop into haploid gametophytes
by mitosis and produce haploid gametes
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Haploid
Gametophyte
(n)
Mitosis
Spore
Sperm
Egg
n n
n n Spores
Meiosis
Gamete fusion
Spore mother
2n cell
2n Zygote
2n Embryo
Sporangia
Sporophyte
(2n)
Diploid
Mosses, Liverworts, and Hornworts
• Nonvascular plants are
divided into three major
phyla-Bryophyta,
Hepaticophyta, and
Anthocerophyta- with all
members being relatively
unspecialized but
collectively able to inhabit
diverse environments
Mosses
• The leaf like
structures belong to
the gametophyte.
Each of the yellowish
brown stalks with a
capsule at is summit
is a sporophyte
Liverworts
• The sporophytes are
formed by fertilization
within the tissues of
the umbrella-shaped
structures that arise
from the surface of
the flat green,
creeping,
gametophyte
Hornworts
• Unlike the
sporophytes of other
bryophytes, most
hornworts
sporophytes are
photosynthetic
Seedless Vascular Plants
• Seedless vascular
plants have welldeveloped conducting
tissues in their
sporophytes.
• The first vascular plants for which we have a
relatively complete record of belonged to the phylum
Rhyniophya.
• They flourished some 410 million years ago but are
now extinct.
• These plants were homosporous (only produce
one type of spore for reproduction; asexual).
• Seeds only occur in heterosporous plants (two
types of spores for reproduction; sexual).
• Eventually these ancient vascular plants evolved
more complex arrangements, leading to the
formation of real leaves.
• Early plants soon began to develop vascular
tissues that acted as efficient water and food
conducting systems.
• These consist of strands of specialized
cylindrical or elongated cells that form a network
throughout a plant, extending from near the tips
of the roots, through the stems, and into true
leaves.
• The seven living phyla of vascular plants
dominate terrestrial habitats everywhere,
except for the highest of mountains and
the tundra.
• Most vascular plants have well-developed
conducting tissues, specialized stems,
leaves, roots, cuticles, and stomata. Many
have seeds, which protect embryos until
conditions are suitable for further
development.
• Earliest vascular plants lacked seeds.
• Two phyla of seedless vascular plants:
•
•
Lycophyta  Club mosses (relicts of an ancient past when
vascular plants first evolved.)
Pterophyta  Whisk ferns, Horsetails, and Ferns.
– All reproduce using sporophytes (asexually).
• In modern vascular plants, the gametophytes
have been reduced in size and complexity,
individuals have specialized tissues.
• Gametophytes are the phases where gametes
are produced for sexual reproduction (two
parts).
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Archegonium
Mitosis
Antheridium
Rhizoids
Spore Gametophyte
n Sperm
MEIOSIS
FERTILIZATION
2n
Mature
sporangium Mature
frond
Egg
Embryo
Sorus (cluster
of sporangia)
Leaf of young
sporophyte
Adult
sporophyte
Rhizome
Gametophyte
Seed Plants
• First appeared 425 million years ago
• Descended from spore-bearing plants
called progymnosperms
• This common ancestor gave way to
gymnosperms and angiosperms
Formation
• Embryo is protected by extra tissue,
creating an ovule
• Tissue hardens to form seed coat
• This protects the embryo from drought and
helps disperse the seed
• Presence of seeds introduced dormant
phase- allows embryo to survive until
conditions are better
Reproduction
• 2 kinds of gametophytes- male and female
• In seed plants, the sperm moves to the
egg through a pollen tube eliminating the
need for external water
• Unlike seedless plants, whole male
gametophyte moves to female
• Female gametophyte develops in ovule
Gymnosperms- “naked-seeded
plants”
• Cone-bearing seed
plants; ovules not
completely enclosed
at time of pollination
• 4 groups: conifers,
cycads, gnetophytes,
and Ginkgo
• Can range from 25g
to 45 kg and mm’s to
over a m
Conifers
• Ex. Pines, spruces, firs, cedars, hemlocks,
yews, larches, cypresses, and others
• Found in colder temperate and drier
regions
• Sources of timber, paper, resin, taxol, and
other products
Pines
• Over 100 species exist
• Tough, needlelike leaves
produced in clusters of 2
to 5
• Thick cuticle and
recessed stomataadaptation for preventing
water loss
• Secrete resin used in
turpentine and rosin
• Wood consists of xylem
and is considered ‘soft’
Reproduction- Males
• Seed plants are heterosporus so spores give
rise to two types of gametophytes
• Male gametophytes develop from microspores
• A pair of microsporangia form sacs in which
numerous ‘mother’ cells undergo meiosis
creating 4 microspores
• Develop into 4-celed pollen grains with air sacs
• Single cluster of male pine cones can produce
over 1 million pollen grains
Reproduction- Female
• Two ovules develop near base and contain
megasporangium called nucellus
• Nucellus is surrounded by cells called the
integument with small opening called the
micropyle
• Single megaspore mother within each
megasporangium undergoes meiosis and
becomes 4 megapsores
• Only one survives and develops into female
gametophyte and can contain thousands of cells
Pollination
• Pollen is drawn into microphyle
• While female is developing, pollen makes
its way through nucellus
• One of the pollen’s 4 cells divide through
mitosis and one of these two divides again
• Final cells are sperm
• 15 months after pollinations, zygote is
formed
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Pollen
tube
Megaspore
Mature seed
cone (2nd year)
Mitosis
Pollination
Pollen FERTILIZATION
(15 months after
n pollination)
Mitosis
Mitosis
Embryo
Microspores
Longisection of
seed, showing
Microspore
mother cell 2n embryo Pine
seed
Pollen-bearing
Scale
Mitosis
cone
Megaspore
mother cell
Seedling
Scale
Ovulate (seed-bearing)
cone
Sporophyte
Cycads (Cycadophyta)
• Slow-growing in tropical
and subtropical regions
• Life cycle similar to pines
• Sperm is formed within
pollen tube and released
within ovule to
archegonium
• Sperm cells are largest
among living organisms
Gnetophytes (Gnetophyta)
• 3 genera, 65 species
• Only gymnosperms
with vessels in xylem
• Over half are in genus
Ephedra and plants
are shrubby and have
scalelike leaves
• Species of genus
Gnetum are vineline
with broad leaves
Ginkgo (Ginkgophyta)
• Only one living species
remains
• Name comes from fanshaped leaves
• Sperm have flagella and
ginkgo is dioecious- male
and female reproductive
structure produced on
different trees
• Resistant to air pollution
Angiosperms- “Vessel seed”
• Flowering plants;
ovules completely
enclosed in tissue
• 250,000 known
species
• Vessel in name refers
to carpal- modified
leaf that encapsulates
seeds
Origins
• Fossils as old as 125
million years old
• Known to be
angiosperms because
fossils have both
male and female
reproductive
structures
• Lack petals and
sepals that evolved
later
Monocots and Eudicots
• Eudicots (175,000)more primitive; 1/6 of
species are annuals;
mints, peas,
sundlowers
• Monocots (65,000)lilies, cattails, orchids;
few are annual; have
no ‘true’ wood
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Structure of flowers
Stamen
Stigma
Style
Carpel
Ovule
Ovary
Anther
Filament
Petal
Sepal
Receptacle
Pedicel
Megaspore
mother cell
Nucellus
Integuments
Micropyle
Stalk of
Ovule
(funiculus)
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Life Cycle
Microspore
mother cells (2n)
MEIOSIS
Anther (2n)
Stigma
Anther
Ovary
Adult
sporophyte
with flower
(2n)
Generative cell
Tube nucleus
Mitosis
Microspores (n)
Pollen grains
Megaspore
(microgametophytes) (n)
mother cell (2n)
Megaspore (n)
MEIOSIS
Egg
Mitosis
Sperm
Tube
nucleus
Pollen
tube
Style
Ovule
8-nucleate
2n
n
embryo sac
DOUBLE FERTILIZATION (megagametophyte) (n)
Embryo (2n)
Seed coat
Germination
Young
sporophyte
(2n)
Cotyledons
Polar
nuclei
Egg
Seed (2n)
Endosperm (3n)
Sperm
Formation
of pollen
tube (n)