Plant Diversity II The Evolution of Seed Plants

1
Plant Diversity IIThe Evolution of Seed Plants

• Chapter 30

2
Plant Origins
Land plants
Vascular plants
Bryophytes (nonvascular plants)
Seedless vascular plants
Seed plants
Seed plants appeared 360 m.y.a. with the rise of
the Gymnosperms
Mosses
Liverworts
Hornworts
Angiosperms
Gymnosperms
Lycophytes (club mosses etc.)
Charophyceans
Pterophyte (ferns, horsetails, whisk fern)
Origin of seed plants (about 360 mya)
Flowering plants (Angiosperms) the other
surviving lineage appeared 200 million years
later
Origin of vascular plants (about 420 mya)
Origin of land plants (about 475 mya)
Ancestral green alga
Hashed lines indicate uncertainties
Fig. 29.7
3
Bryophytes Gametophyte dominant sporophyte
dependent gametophyte independent
Fig. 30.2
4
Seedless vascularplants Sporophyte dominant
sporophyte initially dependent gametophyte
independent
Bryophytes Gametophyte dominant sporophyte
dependent gametophyte independent
Fig. 30.2
5
Seedless vascularplants Sporophyte dominant
sporophyte initially dependent gametophyte
independent
Bryophytes Gametophyte dominant sporophyte
dependent gametophyte independent
Seed plants Sporophyte dominant sporophyte
independent gametophyte dependent microscopic
GymnospermsGametophytes develop inside cones
AngiospermsGametophytes develop inside flowers
Fig. 30.2
6
Seedless vascularplants Sporophyte dominant
sporophyte initially dependent gametophyte
independent
Bryophytes Gametophyte dominant sporophyte
dependent gametophyte independent
Seed plants Sporophyte dominant sporophyte
independent gametophyte dependent microscopic
Gametophytes develop from spores retained within
sporangia of the parental sporophyte
Fig. 30.2
7
Seed plants
See diagram on pg. 586
Heterosporous spore production (some seedless
vascular plants all seed plants)
Megasporangium in megasporophyll (2n)
Female Gametophyte (n)
Megaspore (n)
Eggs (n)
Microsporangium in microsporophyll (2n)
Male Gametophyte (n)
Microspore (n)
Sperm (n)
8
Seed plants
Layers of integuments envelope and protect the
megasporangium
In this example we are using a pine cone
Integument
Spore wall
A megaspore develops into a multicellular female
gametophyte
Megasporangium (2n)
Megaspore (n)
The whole structure megasporangium, megaspore,
and integuments is called an ovule
Unfertilized ovule
Fig. 30.3
9
Seed plants
Fertilization initiates the transformation of the
ovule into a seed
Female gametophyte (n)
Spore wall
A megaspore develops into a multicellular female
gametophyte
Egg nucleus (n)
Discharged sperm nucleus (n)
Micropyle
Male gametophyte (pollen grain) (n)
Fig. 30.3
10
Seed plants
Fertilization initiates the transformation of the
ovule into a seed
Seed coat (derived from Integument)
Compared to a single-celled spore, a seed is much
more resistant and complex
Food supply
Embryo (2n) (new sporophyte)
Fig. 30.3
11
Gymnosperms
Naked seedsnot enclosed by an ovary and
develop on the surface of modified leaves that
usually form cones (strobili)
12
Gymnosperms
Phylum Ginkgophyta Ginkgo biloba is the only
living species of this entire phylum
13
Gymnosperms
Phylum Cycadophyta(cycads, sago palms) Thrived
during the Age of Dinosaurs only 130 species
alive today
14
Gymnosperms
Phylum Cycadophyta(cycads, sago palms) Thrived
during the Age of Dinosaurs only 130 species
alive today
?
?
15
Gymnosperms
Phylum Gnetophyta 3 genera Gnetum
16
Gymnosperms
Phylum Gnetophyta 3 genera Gnetum Ephedra
17
Gymnosperms
Phylum Gnetophyta 3 genera Gnetum Ephedra Wel
witschia
18
Gymnosperms
Phylum Coniferophyta E.g., longleaf pine
19
Gymnosperms
Phylum Coniferophyta E.g., longleaf pine
KEH note For future this might be a good place
to stop and give an overview of my research and
the plight of longleaf.
20
Gymnosperms
Phylum Coniferophyta E.g., longleaf pine, giant
sequoia
21
Gymnosperms
Phylum Coniferophyta E.g., longleaf pine, giant
sequoia, cypress
22
Gymnosperms
Phylum Coniferophyta E.g., longleaf pine,
sequoia, cypress, and 600 other cone-bearing
species
23
Gymnosperms(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulatecone
Megasporangium
Megasporangia and microsporangia are found in
separate cones
Gametophytes
Pollencone
Megasporocyte
Meiosis
Meiosis
Meiosis produces spores and begins the haploid
generation
Microsporocyte
Microsporangium
Megasporocytes (2n) are the cells within
megasporangia that undergo meiosis to produce
megaspores (n)
Egg
Microsporocytes (2n) are the cells within
microsporangia that undergo meiosis to produce
microspores (n)
Fig. 30.6
Fertilization
24
Gymnosperms(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulatecone
Megasporangium
Gametophytes
Pollencone
Megasporocyte
Meiosis
Meiosis
Each megaspore develops into a female
gametophyte
Microsporocyte
Microsporangium
Pollen
Each microspore develops into a male gametophyte
(a pollen grain)
Megaspore
Egg
A pollen grain gains access to a female
gametophyte through a micropyle
Fig. 30.6
Fertilization
25
Gymnosperms(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulatecone
Megasporangium
Gametophytes
Pollencone
Megasporocyte
Meiosis
Meiosis
The female gametophyte contains 2 or 3
archegonia, each with 1 egg cell
Microsporocyte
Microsporangium
Pollen
Megaspore
Two cells of the male gametophyte are sperm
Archegonium
Egg nuclei
Sperm nuclei
Fig. 30.6
Fertilization
26
Gymnosperms(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulatecone
Megasporangium
Fertilization (union of 1 egg and 1 sperm)
produces an embryo
Gametophytes
Pollencone
Megasporocyte
Meiosis
Meiosis
Microsporocyte
Microsporangium
Pollen
Megaspore
Archegonium
Egg nuclei
Sperm nuclei
Embryo
Fig. 30.6
Fertilization
27
Gymnosperms(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulatecone
Megasporangium
Fertilization (union of 1 egg and 1 sperm)
produces an embryo
Gametophytes
Pollencone
Megasporocyte
Meiosis
Meiosis
Embryos develop within seeds
Microsporocyte
Microsporangium
Seedling
Pollen
Seeds germinate and embryos become seedlings
Megaspore
Archegonium
Seed
Egg nuclei
Sperm nuclei
Embryo
Fig. 30.6
Fertilization
28
Plant Origins
Land plants
Vascular plants
Bryophytes (nonvascular plants)
Seedless vascular plants
Seed plants
Seed plants appeared 360 m.y.a. with the rise of
the Gymnosperms
Mosses
Liverworts
Hornworts
Angiosperms
Gymnosperms
Lycophytes (club mosses etc.)
Charophyceans
Pterophyte (ferns, horsetails, whisk fern)
Origin of seed plants (about 360 mya)
Flowering plants (Angiosperms) the other
surviving lineage appeared 200 million years
later
Origin of vascular plants (about 420 mya)
Origin of land plants (about 475 mya)
Ancestral green alga
Hashed lines indicate uncertainties
Fig. 29.7
29
Angiosperms
Flowering plantsseeds develop inside sporophyte
ovaries
30
Angiosperms
BASAL ANGIOSPERMS
Flowering plantsseeds develop inside sporophyte
ovaries
Amborella trichopoda
Water lily
Star anise
250,000 extant species
HYPOTHETICAL TREE OF FLOWERING PLANTS
Eudicots
Star anise
Monocots
Magnoliids
Water lilies
Amborella
6 main clades (see pg. 602)
Magnolia grandiflora
31
Angiosperms(a.k.a., flowering plants)
(?)
Carpel
Stigma
Style
Ovary
Petal
Anther
Filament
Sepal
(?)
Stamen
Ovule
Receptacle
Fig. 30.7
32
Angiosperms
Complete flowers have sepals, petals, stamens
carpels
See Fig. 30.7
33
Angiosperms
Complete flowers have sepals, petals, stamens
carpels
See Fig. 30.7
34
Angiosperms
Complete flowers have sepals, petals, stamens
carpels
See Fig. 30.7
35
Angiosperms
Complete flowers have sepals, petals, stamens
carpels
Ovules
See Fig. 30.7
36
Angiosperms
Complete flowers have sepals, petals, stamens
carpels
Bisexual flowers have both male (stamens) and
female (carpels) reproductive structures so
complete flowers are also bisexual
See Fig. 30.7
37
Angiosperms
Incomplete flowers lack one or more of the
following sepals, petals, stamens or carpels
E.g., most grasses lack petals
38
Angiosperms
Self-fertilization
Some bisexual flowerscan self-fertilize
See Fig. 30.7
39
Angiosperms
Monoecious individuals have separate male and
female unisexual flowers on the same plant which
helps reduce self-fertilization, but does not
eliminate it
Incomplete, staminate flowers lack carpels
Incomplete, carpellate flowers lack stamens
E.g., squash
40
Angiosperms
Dioecious species have separate male and female
individuals which eliminates the possibility of
self-fertilization
Staminate flowers
Carpellate flowers
E.g., branches from two holly plants
41
Angiosperms
Monocots
Eudicots
1 cotyledon
2 cotyledons
Netlikeveins
Parallelveins
Scatteredvascular tissue
Ring of v. tissue
Fibrous roots
Tap root
1 openingin pollen
3 openingsin pollen
Floral organs in 3s
Floral organsin 4s or 5s
See Fig. 30.12
42
Angiosperms
Key
Haploid
Diploid
Microsporangium
Anthers contain microsporangia that produce
microspores
Microspore
Meiosis
Pollen
Each microspore forms a pollen grain (a male
gametophyte)
Sporophyte
Meiosis
Megasporangium
Gametophytes
Ovules contain megasporangia that produce
megaspores
Megaspore
Embryo sac
Each megaspore forms an embryo sac (a female
gametophyte)
Fertilization
Fig. 30.10
43
Angiosperms
Key
Haploid
Diploid
Microsporangium
Pollen disperses to stigmas
Microspore
Meiosis
Double fertilization is unique to angiosperms
Pollen
Sporophyte
Seedling
Sperm enter an ovule through a micropyle
Meiosis
Megasporangium
Gametophytes
Megaspore
From a single pollen grain, one sperm unites with
the egg to produce a zygote
Embryo
Embryo sac
Egg
the second sperm unites with 2 nuclei of the
embryo sac to produce triploid (3n) endosperm
Zygote
2 sperm
Fertilization
Fig. 30.10
Endosperm
44
Some key points to remember
All spores and gametes are haploid
Sporophytes are diploid, and produce spores
Gametophytes are haploid, and produce gametes
Sporophyte (2n) (If heterosporous
separate mega microsporangia and two
types of spores if homosporous single
type of sporangia and single type of
spore)
meiosis
Spores (1n)
Gametes (1n)
Gametophyte (1n) (If bryophyte, seedless
vascular or gymnosperm, archegonia
antheridia present)
mitosis
45
Seed plants and human welfare
Humans began practicing agriculture only about
18,000 years ago
Multiple independent origins
46
Seed plants and human welfare
Even so, most of our food currentlycomes from
angiosperms
Just 6 crops wheat, rice, maize (corn),
potatoes, cassava (manioc), sweet potatoes
yield 80 of all the calories consumed by humans
47
Seed plants and human welfare
It takes 5 pounds of grain to produce 1 pound
of grain-fed beef