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
Figure 30.1

3. In addition to seeds, the following are common to all seed plants
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. Gametophyte/sporophyte relationships
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)
Microscopic female
gametophytes (n)
inside these parts
of flowers
(dependent)
Microscopic male
gametophytes (n)
inside these parts
of flowers
(dependent)
Microscopic male
gametophytes (n)
in pollen cones
(dependent)
Sporophyte (2n),
the flowering plant
(independent)
Sporophyte (2n)
(independent)
Reduced gametophyte dependent on sporophyte
(seed plants: gymnosperms and angiosperms).
(c)
Figure 30.2a–c

5. 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

6. 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)

7. 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

8. If a pollen grain germinates
It gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule
Female
gametophyte (n)
Egg nucleus (n)
Spore wall
Male gametophyte
(within germinating
pollen grain) (n)
Discharged
sperm nucleus (n)
Pollen grain (n)
Micropyle
(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.
Figure 30.3b

9. 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
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)
Figure 30.3c

10. The gymnosperms include four plant phyla
Cycadophyta
Gingkophyta
Gnetophyta
Coniferophyta

11. Exploring Gymnosperm Diversity
Gnetum
Ephedra
Ovulate cones
Welwitschia
PHYLUM GNETOPHYTA
PHYLUM CYCADOPHYTA
PHYLUM GINKGOPHYTA
Cycas revoluta
Figure 30.4

12. Exploring Gymnosperm Diversity
Douglas fir
Pacific
yew
Common juniper
Wollemia pine
Bristlecone pine
Sequoia
PHYLUM CYCADOPHYTA
Figure 30.4

13. Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits
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

14. Characteristics of Angiosperms
The key adaptations in the evolution of angiosperms
Are flowers and fruits

15. Flowers
The flower
Is an angiosperm structure specialized for sexual reproduction

16. 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
Anther
Filament
Stigma
Style
Ovary
Carpel
Petal
Receptacle
Ovule
Sepal
Stamen
Figure 30.7

17. 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

18. Can be carried by wind, water, or animals to new locations, enhancing seed dispersal
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)
Figure 30.9a–c

19. 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

20. The two main groups of angiosperms
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

21. Dog rose (Rosa canina), a wild rose
Exploring Angiosperm Diversity
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
netlike
usually arranged
in ring
Taproot (main root)
usually present
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 five
Filament
Ovary
Eudicot
MONOCOTS
EUDICOTS
Figure 30.12

22. 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) 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.
Figure 30.13a–c

23. Concept 30.4: Human welfare depends greatly on seed plants
No group is more important to human survival than seed plants

24. Products from Seed Plants
Humans depend on seed plants for
Food
Wood
Many medicines
Table 30.1

25. Threats to Plant Diversity
Destruction of habitat
Is causing extinction of many plant species and the animal species they support

26. The End