- Seed plants evolved reduced gametophytes that develop within spores retained in the parent sporophyte tissue, providing protection. Gymnosperms bear naked seeds typically on cones, while angiosperms bear seeds within fruits and have flowers as specialized reproductive structures. The key adaptations that enabled angiosperm diversification were flowers, which attract pollinators, and fruits, which aid seed dispersal.

1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 30
Plant Diversity II: The
Evolution of Seed Plants

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Feeding the World
• Seeds changed the course of plant evolution
– Enabling their bearers to become the dominant
producers in most terrestrial ecosystems
Figure 30.1

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 30.1: The reduced gametophytes of
seed plants are protected in ovules and pollen
grains
• In addition to seeds, the following are common
to all seed plants
– Reduced gametophytes
– Heterospory
– Ovules
– Pollen

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Advantages of Reduced Gametophytes
• The gametophytes of seed plants
– Develop within the walls of spores retained
within tissues of the parent sporophyte

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Gametophyte/sporophyte relationships
Figure 30.2a–c
Sporophyte dependent
on gametophyte
(mosses and other
bryophytes).
(a) Large sporophyte and
small, independent
gametophyte (ferns
and other seedless
vascular plants).
(b)
Microscopic female
gametophytes (n) in
ovulate cones
(dependent)
Sporophyte (2n),
the flowering plant
(independent)
Microscopic male
gametophytes (n)
inside these parts
of flowers
(dependent)
Microscopic male
gametophytes (n)
in pollen cones
(dependent) Sporophyte (2n)
(independent)
Microscopic
female
gametophytes (n)
inside these parts
of flowers
(dependent)
Reduced gametophyte dependent on sporophyte
(seed plants: gymnosperms and angiosperms).
(c)
Gametophyte
(n)
Gametophyte
(n)
Sporophyte
(2n)
Sporophyte
(2n)

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Heterospory: The Rule Among Seed Plants
• Seed plants evolved from plants that had
megasporangia
– Which produce megaspores that give rise to
female gametophytes
• Seed plants evolved from plants that had
microsporangia
– Which produce microspores that give rise to
male gametophytes

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ovules and Production of Eggs
• An ovule consists of
– A megasporangium, megaspore, and
protective integuments
Figure 30.3a
(a) Unfertilized ovule. In this sectional
view through the ovule of a pine (a
gymnosperm), a fleshy
megasporangium is surrounded by a
protective layer of tissue called an
integument. (Angiosperms have two
integuments.)
Integument
Spore wall
Megasporangium
(2n)
Megaspore (n)

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Pollen and Production of Sperm
• Microspores develop into pollen grains
– Which contain the male gametophytes of
plants
• Pollination
– Is the transfer of pollen to the part of a seed
plant containing the ovules

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• If a pollen grain germinates
– It gives rise to a pollen tube that discharges two
sperm into the female gametophyte within the
ovule
Figure 30.3b
(b) Fertilized ovule. A megaspore develops into a
multicellular female gametophyte. The micropyle,
the only opening through the integument, allows
entry of a pollen grain. The pollen grain contains a
male gametophyte, which develops a pollen tube
that discharges sperm.
Spore wall
Male gametophyte
(within germinating
pollen grain) (n)
Female
gametophyte (n)
Egg nucleus (n)
Discharged
sperm nucleus (n)
Pollen grain (n)Micropyle

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Pollen, which can be dispersed by air or
animals
– Eliminated the water requirement for
fertilization

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Evolutionary Advantage of Seeds
• A seed
– Develops from the whole ovule
– Is a sporophyte embryo, along with its food
supply, packaged in a protective coat
Figure 30.3c
Gymnosperm seed. Fertilization initiates
the transformation of the ovule into a
seed,
which consists of a sporophyte embryo, a
food supply, and a protective seed coat
derived from the integument.
(c)
Seed coat
(derived from
Integument)
Food supply
(female
gametophyte
tissue) (n)
Embryo (2n)
(new sporophyte)

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 30.2: Gymnosperms bear “naked”
seeds, typically on cones
• Among the gymnosperms are many well-
known conifers
– Or cone-bearing trees, including pine, fir, and
redwood

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The gymnosperms include four plant phyla
– Cycadophyta
– Gingkophyta
– Gnetophyta
– Coniferophyta

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Exploring Gymnosperm Diversity
Figure 30.4
Gnetum
Ephedra
Ovulate cones
Welwitschia
PHYLUM GNETOPHYTA
PHYLUM CYCADOPHYTA PHYLUM GINKGOPHYTA
Cycas revoluta

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Exploring Gymnosperm Diversity
Figure 30.4
Douglas fir
Pacific
yew
Common juniper
Wollemia pine
Bristlecone pine Sequoia
PHYLUM CYCADOPHYTA

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gymnosperm Evolution
• Fossil evidence reveals that by the late Devonian
– Some plants, called progymnosperms, had begun
to acquire some adaptations that characterize
seed plants
Figure 30.5

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Gymnosperms appear early in the fossil record
– And dominated the Mesozoic terrestrial
ecosystems
• Living seed plants
– Can be divided into two groups: gymnosperms
and angiosperms

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A Closer Look at the Life Cycle of a Pine
• Key features of the gymnosperm life cycle
include
– Dominance of the sporophyte generation, the
pine tree
– The development of seeds from fertilized
ovules
– The role of pollen in transferring sperm to
ovules

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 30.6
Ovule
Megasporocyte (2n)
Integument
Longitudinal
section of
ovulate cone
Ovulate
cone
Pollen
cone
Mature
sporophyte
(2n)
Longitudinal
section of
pollen cone
Microsporocytes
(2n)
Pollen
grains (n)
(containing male
gametophytes)
MEIOSIS
Micropyle
Germinating
pollen grain
Megasporangium
MEIOSIS
Sporophyll
Microsporangium
Surviving
megaspore (n)
Germinating
pollen grain
Archegonium
IntegumentEgg (n)
Female
gametophyte
Germinating
pollen grain (n)
Discharged
sperm nucleus (n)
Pollen
tube
Egg nucleus (n)
FERTILIZATION
Seed coat
(derived from
parent
sporophyte) (2n)
Food reserves
(gametophyte
tissue) (n)
Embryo
(new sporophyte)
(2n)
Seeds on surface
of ovulate scale
Seedling
Key
Diploid (2n)
Haploid (n)
• The life cycle of a pine
A pollen cone contains many microsporangia
held in sporophylls. Each microsporangium
contains microsporocytes (microspore mother
cells). These undergo meiosis, giving rise to
haploid microspores that develop into
pollen grains.
3
In most
conifer species,
each tree has
both ovulate
and pollen
cones.
1
A pollen grain
enters through
the micropyle
and germinates,
forming a pollen
tube that slowly
digests
through the
megasporangium.
4
While the
pollen tube
develops, the
megasporocyte
(megaspore
mother cell)
undergoes meiosis,
producing four
haploid cells. One
survives as a
megaspore.
5
The female gametophyte
develops within the megaspore
and contains two or three
archegonia, each with an egg.
6
By the time the eggs are mature,
two sperm cells have developed in the
pollen tube, which extends to the
female gametophyte. Fertilization occurs
when sperm and egg nuclei unite.
7
Fertilization usually occurs more
than a year after pollination. All eggs
may be fertilized, but usually only one
zygote develops into an embryo. The
ovule becomes a seed, consisting of an
embryo, food supply, and seed coat.
8
An ovulate cone scale has two
ovules, each containing a mega-
sporangium. Only one ovule is shown.
2

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 30.3: The reproductive adaptations of
angiosperms include flowers and fruits
• Angiosperms
– Are commonly known as flowering plants
– Are seed plants that produce the reproductive
structures called flowers and fruits
– Are the most widespread and diverse of all
plants

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Characteristics of Angiosperms
• The key adaptations in the evolution of
angiosperms
– Are flowers and fruits

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Flowers
• The flower
– Is an angiosperm structure specialized for
sexual reproduction

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A flower is a specialized shoot with modified
leaves
– Sepals, which enclose the flower
– Petals, which are brightly colored and attract
pollinators
– Stamens, which produce pollen
– Carpels, which produce ovules
Figure 30.7
Anther
Filament
Stigma
Style
Ovary
Carpel
Petal
Receptacle
Ovule
Sepal
Stamen

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fruits
• Fruits
– Typically consist of a mature ovary
Figure 30.8a–e
(b) Ruby grapefruit, a fleshy fruit
with a hard outer layer and
soft inner layer of pericarp
(a) Tomato, a fleshy fruit with
soft outer and inner layers
of pericarp
(c) Nectarine, a fleshy
fruit with a soft outer
layer and hard inner
layer (pit) of pericarp
(e) Walnut, a dry fruit that
remains closed at maturity
(d) Milkweed, a dry fruit that
splits open at maturity

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Can be carried by wind, water, or animals to new
locations, enhancing seed dispersal
Figure 30.9a–c
Wings enable maple fruits
to be easily carried by the wind.
(a)
Seeds within berries and other
edible fruits are often dispersed
in animal feces.
(b)
The barbs of cockleburs
facilitate seed dispersal by
allowing the fruits to
“hitchhike” on animals.
(c)

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Angiosperm Life Cycle
• In the angiosperm life cycle
– Double fertilization occurs when a pollen tube
discharges two sperm into the female
gametophyte within an ovule
– One sperm fertilizes the egg, while the other
combines with two nuclei in the center cell of
the female gametophyte and initiates
development of food-storing endosperm
• The endosperm
– Nourishes the developing embryo

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The life cycle of an angiosperm
Figure 30.10
Key
Mature flower on
sporophyte plant
(2n)
Ovule with
megasporangium (2n)
Female gametophyte
(embryo sac)
Nucleus of
developing
endosperm
(3n)
Discharged
sperm nuclei (n)
Pollen
tube
Male gametophyte
(in pollen grain)
Pollen
tube
Sperm
Surviving
megaspore
(n)
Microspore (n) Generative cell
Tube cell
Stigma
Ovary
MEIOSIS
MEIOSIS
Megasporangium
(n)
Pollen
grains
Egg
Nucleus (n)
Zygote (2n)
Antipodal
cells
Polar nuclei
Synergids
Egg (n)
Embryo (2n)
Endosperm
(food
Supply) (3n)
Seed coat (2n)
Seed
FERTILIZATION
Haploid (n)
Diploid (2n)
Anther
Sperm
(n)
Pollen
tube
Style
Microsporangium
Microsporocytes (2n)
Germinating
Seed
Anthers contain microsporangia.
Each microsporangium contains micro-
sporocytes (microspore mother cells) that
divide by meiosis, producing microspores.
1
Microspores form
pollen grains (containing
male gametophytes). The
generative cell will divide
to form two sperm. The
tube cell will produce the
pollen tube.
2
In the megasporangium
of each ovule, the
megasporocyte divides by
meiosis and produces four
megaspores. The surviving
megaspore in each ovule
forms a female gametophyte
(embryo sac).
3
After pollina-
tion, eventually
two sperm nuclei
are discharged in
each ovule.
4
Double fertilization occurs. One sperm
fertilizes the egg, forming a zygote. The
other sperm combines with the two polar
nuclei to form the nucleus of the endosperm,
which is triploid in this example.
5
The zygote
develops into an
embryo that is
packaged along
with food into a
seed. (The fruit
tissues surround-
ing the seed are
not shown).
6
When a seed
germinates, the
embryo develops
into a mature
sporophyte.
7

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Angiosperm Evolution
• Clarifying the origin and diversification of
angiosperms
– Poses fascinating challenges to evolutionary
biologists
• Angiosperms originated at least 140 million
years ago
– And during the late Mesozoic, the major
branches of the clade diverged from their
common ancestor

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fossil Angiosperms
• Primitive fossils of 125-million-year-old
angiosperms
– Display both derived and primitive traits
Figure 30.11a, b
Carpel
Stamen
Archaefructus sinensis, a 125-million-year-
old fossil.
(a)
Artist’s reconstruction of
Archaefructus sinensis
(b)
5 cm

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
An “Evo-Devo” Hypothesis of Flower Origins
• In hypothesizing how pollen-producing and
ovule-producing structures were combined into
a single flower
– Scientist Michael Frohlich proposed that the
ancestor of angiosperms had separate pollen-
producing and ovule-producing structures

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Angiosperm Diversity
• The two main groups of angiosperms
– Are monocots and eudicots
• Basal angiosperms
– Are less derived and include the flowering
plants belonging to the oldest lineages
• Magnoliids
– Share some traits with basal angiosperms but
are more closely related to monocots and
eudicots

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Exploring Angiosperm Diversity
Figure 30.12
Amborella trichopoda Water lily (Nymphaea
“Rene Gerard”)
Star anise (Illicium
floridanum)
BASAL ANGIOSPERMS
HYPOTHETICAL TREE OF FLOWERING PLANTS
MAGNOLIIDS
Amborella
Waterlilies
Staranise
andrelatives
Magnoliids
Monocots
Eudicots
Southern magnolia (Magnolia
grandiflora)

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Exploring Angiosperm Diversity
Figure 30.12
Orchid
(Lemboglossum
fossii)
Monocot
Characteristics
Embryos
Leaf
venation
Stems
Roots
Pollen
Flowers
Pollen grain with
one opening
Root system
Usually fibrous
(no main root)
Vascular tissue
scattered
Veins usually
parallel
One cotyledon Two cotyledons
Veins usually
netlike
Vascular tissue
usually arranged
in ring
Taproot (main root)
usually present
Pollen grain with
three openings
Zucchini
(Cucurbita
Pepo), female
(left) and
male flowers
Pea (Lathyrus
nervosus,
Lord Anson’s
blue pea), a
legume
Dog rose (Rosa canina), a wild rose
Pygmy date palm
(Phoenix roebelenii)
Lily (Lilium
“Enchant-
ment”)
Barley (Hordeum vulgare),
a grass
Anther
Stigma
California
poppy
(Eschscholzia
californica)
Pyrenean oak
(Quercus
pyrenaica)
Floral organs
usually in
multiples of three
Floral organs usually
in multiples of
four or fiveFilament Ovary
Eudicot
Characteristics
MONOCOTS EUDICOTS

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Evolutionary Links Between Angiosperms and Animals
• Pollination of flowers by animals and transport
of seeds by animals
– Are two important relationships in terrestrial
ecosystems
Figure 30.13a–c
(a) A flower pollinated by
honeybees. This honeybee is
harvesting pollen and nectar (a
sugary solution secreted by
flower glands) from a Scottish
broom flower. The flower has a
tripping mechanism that arches
the stamens over the bee
and dusts it with pollen, some of
which will rub off onto the stigma
of the next flower the bee visits.
(c) A flower pollinated by nocturnal animals. Some
angiosperms, such as this cactus, depend mainly on
nocturnal pollinators, including bats. Common
adaptations of such plants include large, light-colored,
highly fragrant flowers that nighttime pollinators can
locate.
(b) A flower pollinated by hummingbirds.
The long, thin beak and tongue of this
rufous hummingbird enable the animal to
probe flowers that secrete nectar deep
within floral tubes. Before the hummer
leaves, anthers will dust its beak and
head feathers with pollen. Many flowers
that are pollinated by birds are red or
pink, colors to which bird eyes are
especially sensitive.

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 30.4: Human welfare depends greatly
on seed plants
• No group is more important to human survival
than seed plants

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Products from Seed Plants
• Humans depend on seed plants for
– Food
– Wood
– Many medicines
Table 30.1

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Threats to Plant Diversity
• Destruction of habitat
– Is causing extinction of many plant species
and the animal species they support