1. Plant Diversity II: The Evolution of Seed Plants
Chapter 30
Plant Diversity II: The Evolution of Seed Plants

2. Overview: Feeding the World
Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems

3. Concept 30.1: The reduced gametophytes of seed plants are protected in ovules and pollen grains
The following are common to all seed plants:
Reduced gametophytes
Embryo protected within seed
Ovule
Pollen

4. Advantages of Reduced Gametophytes
Sporophyte
(2n)
Gametophyte
(n)
Sporophyte dependent on gametophyte (mosses and other bryophytes)
Large sporophyte and small, independent game-tophyte (ferns and other seedless vascular plants)
Microscopic female
gametophytes (n) in
ovulate cones
(dependent)
Microscopic male
inside these parts
of flowers
Sporophyte (2n),
the flowering plant
(independent)
gametophytes (n)
in pollen cones
Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms)
The gametophytes of seed plants develop within the walls of spores retained within tissues of the parent sporophyte

5. Ovules and Production of Eggs
An ovule consists of a megasporangium, megaspore, and one or more protective integuments
Gymnosperm megaspores have one integument
Angiosperm megaspores usually have two integuments
Integument
Megasporangium
(2n)
Megaspore (n)
Unfertilized ovule
Fertilized ovule
Spore wall
Male gametophyte
(within germinating
pollen grain) (n)
Micropyle
Female
gametophyte (n)
Egg nucleus (n)
Discharged
sperm nucleus (n)
Pollen grain (n)
Seed coat
(derived from
integument)
Embryo (2n)
(new sporophyte)
Gymnosperm seed
Food supply
(female
gametophyte
tissue) (n)

6. Ovules and Production of Eggs
Diagrammatic ovules. a, Angiosperm ovule. b, Gymnosperm ovule. i, integument (covering); ii, inner integument; m, micropyle (opening); oi, outer integument; s, stalk.

7. Pollen and Production of Sperm
Microspores develop into pollen grains, which contain the male gametophytes
If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule
Integument
Megasporangium
(2n)
Megaspore (n)
Unfertilized ovule
Fertilized ovule
Spore wall
Male gametophyte
(within germinating
pollen grain) (n)
Micropyle
Female
gametophyte (n)
Egg nucleus (n)
Discharged
sperm nucleus (n)
Pollen grain (n)
Seed coat
(derived from
integument)
Embryo (2n)
(new sporophyte)
Gymnosperm seed
Food supply
(female
gametophyte
tissue) (n)

8. The Evolutionary Advantage of Seeds
A seed develops from the whole ovule
A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat

9. Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones
The gymnosperms include four phyla:
Cycadophyta (cycads)
Gingkophyta (one living species: Ginkgo biloba)
Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia)
Coniferophyta (conifers, such as pine, fir, and redwood)

10. LE 30-4aa
Cycas revoluta

11. LE 30-4ab

12. LE 30-4ac

13. LE 30-4ad
Gnetum. This genus includes about 35 species of tropical trees, shrubs, and vines, mainly native to Africa and Asia. Their leaves look similar to those of flowering plants, and their seeds look somewhat like fruits.

14. LE 30-4ae
Ephedra. This genus includes about 40 species that inhabit arid regions throughout the world. Known in North America as “Mormon tea,” these desert shrubs produce the compound ephedrine, commonly used as a decongestant.

15. LE 30-4af
Welwitschia. This genus consists of one species Welwitschia mirabilis, a plant that lives only in the deserts of southwestern Africa. Its strap like leaves are among the largest known.

16. LE 30-4ag
Ovulate
cones

17. LE 30-4ba
Douglas fir. “Doug fir” (Pseudotsuga menziesii) provides more timber than any other North American tree species. Some uses include house framing, plywood, pulpwood for paper, railroad ties, and boxes and crates.

18. Pacific yew. The bark of Pacific yew (Taxa brevifolia) is a
LE 30-4bb
Pacific yew. The
bark of Pacific yew
(Taxa brevifolia) is a
source of taxol, a
compound used to
treat women with
ovarian cancer. The
leaves of a
European yew
species produce a
similar compound,
which can be
harvested without
destroying the plants. Pharmaceutical companies are now refining techniques for synthesizing drugs with taxol-like properties.

19. LE 30-4bc
Bristlecone pine. This species (Pinus longaeva), which is found in the White Mountains of California, includes some of the oldest living organisms, reaching ages of more than 4,600 years. One tree (not shown here) is called Methuselah because it may be the world’s oldest living tree. In order to protect the tree, scientists keep its location a secret.

20. LE 30-4bd
Sequoia. This giant sequoia (Sequoiadendron giganteum), in California’s Sequoia National Park weighs about 2,500 metric tons, equivalent to about 24 blue whales (the largest animals), or 40,000 people. Giant sequoias are the largest living organisms and also some of the most ancient, with some estimated to be between 1,800 and 2,700 years old. Their cousins, the coast redwoods (Sequoia sempervirens), grow to heights of more than 110 meters (taller than the Statue of Liberty) and are found only in a narrow coastal strip of northern California.

21. LE 30-4be
Common juniper. The “berries” of the common juniper (Juniperus communis), are actually ovule-producing cones consisting of fleshy sporophylls.

22. Wollemia pine. Survivors of a confer group
LE 30-4bf
Wollemia pine. Survivors of a confer group
once known only from fossils, living Wollemia
pines (Wollemia nobilis), were discovered in
1994 in a national park
only 150 kilometers
from Sydney, Australia.
The species consists of
just 40 known
individuals in two small
groves. The inset photo
compares the leaves of
this “living fossil” with
actual fossils.

23. Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems
Living seed plants can be divided into two clades: gymnosperms and angiosperms

24. A Closer Look at the Life Cycle of a Pine
Key features of the gymnosperm life cycle:
Dominance of the sporophyte generation
Development of seeds from fertilized ovules
The transfer of sperm to ovules by pollen
The life cycle of a pine is an example
Animation: Pine Life Cycle

25. LE 30-6_3 Key Haploid (n) Diploid (2n) Ovule Ovulate cone
Megasporocyte (2n)
Integument
Longitudinal
section of
ovulate cone
Micropyle
Pollen
cone
Megasporangium
Mature
sporophyte
(2n)
Microsporocytes
(2n)
Germinating
pollen grain
Pollen
grains (n)
(containing male
gametophytes)
MEIOSIS
MEIOSIS
Longitudinal
section of
pollen cone
Surviving
megaspore (n)
Sporophyll
Microsporangium
Seedling
Germinating
pollen grain
Archegonium
Integument
Egg (n)
Seeds on surface
of ovulate scale
Female
gametophyte
Germinating
pollen grain (n)
Food reserves
(gametophyte
tissue) (n)
Seed coat
(derived from
parent
sporophyte) (2n)
Discharged
sperm nucleus (n)
Pollen
tube
Embryo
(new sporophyte)
(2n)
FERTILIZATION
Egg nucleus (n)

26. Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits
Angiosperms are flowering plants
These seed plants have reproductive structures called flowers and fruits
They are the most widespread and diverse of all plants

27. Characteristics of Angiosperms
All angiosperms are classified in a single phylum, Anthophyta
The name comes from the Greek anthos, flower

28. Flowers
The flower is an angiosperm structure specialized for sexual reproduction
A flower is a specialized shoot with up to four types of modified leaves:
Sepals, which enclose the flower
Petals, which are brightly colored and attract pollinators
Stamens, which produce pollen
Carpels, which produce ovules

29. Video: Flower Blooming (time lapse)
LE 30-7
Stigma
Carpel
Stamen
Anther
Style
Filament
Ovary
Petal
Sepal
Ovule
Receptacle
Video: Flower Blooming (time lapse)

30. Animation: Fruit Development
Fruits
A fruit typically consists of a mature ovary but can also include other flower parts
Fruits protect seeds and aid in their dispersal
Mature fruits can be either fleshy or dry
Animation: Fruit Development

31. LE 30-8 Ruby grapefruit, a fleshy fruit
with a hard outer layer and soft
inner layer of pericarp
Tomato, a fleshy fruit with soft
outer and inner layers of pericarp
Nectarine, a fleshy
fruit with a soft outer
layer and hard inner
layer (pit) of pericarp
Milkweed, a dry fruit that splits
open at maturity
Walnut, a dry fruit that remains
closed at maturity

32. LE 30-9
Wings enable maple
fruits to be easily
carried by the wind.
Seeds within berries and other edible fruits are often dispersed in animal feces.
The barbs of cockleburs facilitate seed dispersal by allowing these fruits to hitchhike on animals.

33. The Angiosperm Life Cycle
In the angiosperm life cycle, double fertilization occurs.
ovum
food-storing endosperm
nourishes the developing embryo

34. LE 30-10a Key Haploid (n) Diploid (2n) Microsporangium Anther
Microsporocytes (2n)
Mature flower on
Sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Generative cell
Ovule with
megasporangium (2n)
Tube cell
Male
gametophyte
(in pollen
grain)
Ovary
MEIOSIS
Megasporangium
(n)
Surviving
megaspore
(n)
Antipodal cells
Female gametophyte
(embryo sac)
Polar nuclei
Pollen
tube
Synergids
Eggs (n)
Sperm
(n)

35. LE 30-10b Key Haploid (n) Diploid (2n) Microsporangium Anther
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Generative cell
Ovule with
megasporangium (2n)
Male
gametophyte
(in pollen
grain)
Tube cell
Ovary
Pollen
grains
MEIOSIS
Stigma
Pollen
tube
Megasporangium
(n)
Sperm
Surviving
megaspore
(n)
Pollen
tube
Style
Female gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
Pollen
tube
Synergids
Eggs (n)
Sperm
(n)
Eggs
nucleus (n)
Discharged
sperm nuclei (n)

36. LE 30-10c Key Haploid (n) Diploid (2n) Microsporangium Anther
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Generative cell
Ovule with
megasporangium (2n)
Male
gametophyte
(in pollen
grain)
Tube cell
Ovary
Pollen
grains
Germinating
seed
MEIOSIS
Stigma
Pollen
tube
Megasporangium
(n)
Embryo (2n)
Sperm
Surviving
megaspore
(n)
Endosperm
(food
supply) (3n)
Seed
Pollen
tube
Seed coat (2n)
Style
Female gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
Pollen
tube
Synergids
Eggs (n)
Zygote (2n)
Sperm
(n)
Nucleus of
developing
endosperm
(3n)
Eggs
nucleus (n)
FERTILIZATION
Discharged
sperm nuclei (n)

37. Animation: Plant Fertilization
Animation: Seed Development
Video: Flowering Plant Life Cycle (time lapse)

38. Angiosperm Evolution
Clarifying the origin and diversification of angiosperms poses fascinating challenges to evolutionary biologists
Angiosperms originated at least 140 million years ago
During the late Mesozoic, the major branches of the clade diverged from their common ancestor

39. Archaefructus sinensis, a 125-million-year-old fossil
LE 30-11
Carpel
Stamen
5 cm
Archaefructus sinensis, a
125-million-year-old fossil
Artist’s reconstruction of
Archaefructus sinensis

40. 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

41. BASAL ANGIOSPERMS Amborella trichopoda Water lily (Nymphaea
LE 30-12aa
BASAL ANGIOSPERMS
Amborella trichopoda
Water lily (Nymphaea
“Rene Gerald”)
Star anise (Illicium
floridanum)

42. HYPOTHETICAL TREE OF FLOWERING PLANTS
LE 30-12ab
HYPOTHETICAL TREE OF FLOWERING PLANTS
Star anise
and relatives
Amborella
Water lilies
Magnoliids
Monocots
Eudicots
MAGNOLIIDS
Southern magnolia
(Magnolia
grandiflora)

43. LE 30-12ba MONOCOTS EUDICOTS Orchid California (Lemboglossum Monocot
rossii)
Monocot
Characteristics
Eudicot
Characteristics
California
poppy
(Eschscholzia
california)
Embryos
One cotyledon
Two cotyledons

44. LE 30-12bb MONOCOTS EUDICOTS Pyrenean oak Leaf (Quercus venation
pyrenaica)
Leaf
venation
Veins usually
netlike
Veins usually
parallel
Stems
Pygmy date palm (Phoenix roebelenii)
Vascular tissue
usually arranged
in ring
Vascular tissue
scattered

45. LE 30-12bc MONOCOTS EUDICOTS Lily (Lilium “Enchantment”) Roots
Dog rose (Rosa canina), a wild rose
Root system
usually fibrous
(no main root)
Taproot (main root)
usually present

46. LE 30-12bd MONOCOTS EUDICOTS Barley (Hordeum vulgare), a grass Pea
(Lathyrusner
vosus, Lord
Anson’s
blue pea),
a legume
Pollen
Pollen grain with
one opening
Pollen grain with
three openings
Flowers
Anther
Zucchini
(Cucurbita
Pepo), female
(left), and
male flowers
Floral organs
usually in
multiples of three
Stigma
Floral organs usually
in multiples of
four or five
Filament
Ovary

47. Evolutionary Links Between Angiosperms and Animals
Pollination of flowers by animals and transport of seeds by animals are two important relationships in terrestrial ecosystems
A flower pollinated by
honeybees.
hummingbirds.
A flower pollinated by nocturnal animals.
Video: Bee Pollinating
Video: Bat Pollinating