Transcript Plant Diversity - Colonization of Land

Chapter 30
Plant Diversity II
The Evolution of Seed Plants
Plant Origins
Land plants
Flowering plants
(Angiosperms) –
the other surviving
lineage – appeared
~200 million years
later
Vascular plants
Angiosperms
Seed plants
Gymnosperms
Pterophyte
(ferns, horsetails, whisk fern)
Seedless vascular plants
Lycophytes
(club mosses etc.)
Mosses
Hornworts
Liverworts
Seed plants
appeared ~360
m.y.a. with the rise
of the
Gymnosperms
Charophyceans
Bryophytes
(nonvascular plants)
Origin of seed plants
(about 360 mya)
Origin of vascular
plants (about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
Hashed lines indicate uncertainties
Fig. 29.7
Bryophytes
Gametophyte dominant;
sporophyte dependent;
gametophyte
independent
Fig. 30.2
Seedless vascular
plants
Bryophytes
Gametophyte dominant;
sporophyte dependent;
gametophyte
independent
Sporophyte dominant;
sporophyte initially
dependent;
gametophyte
independent
Fig. 30.2
Seedless vascular
plants
Bryophytes
Gametophyte dominant;
sporophyte dependent;
gametophyte
independent
Sporophyte dominant;
sporophyte initially
dependent;
gametophyte
independent
Seed plants
Gymnosperms
Sporophyte dominant;
sporophyte independent;
gametophyte
dependent & microscopic
Gametophytes develop
inside cones
Angiosperms
Gametophytes develop
inside flowers
Fig. 30.2
Seedless vascular
plants
Bryophytes
Gametophyte dominant;
sporophyte dependent;
gametophyte
independent
Sporophyte dominant;
sporophyte initially
dependent;
gametophyte
independent
Seed plants
Gametophytes develop
from spores retained
within sporangia of the
parental sporophyte
Sporophyte dominant;
sporophyte independent;
gametophyte
dependent & microscopic
Fig. 30.2
Seed plants
See diagram on pg. 586
Heterosporous spore production
(some seedless vascular plants; all seed plants)
Megasporangium
in megasporophyll
(2n)
Megaspore
(n)
Female
Gametophyte
(n)
Eggs
(n)
Microsporangium
in microsporophyll
(2n)
Microspore
(n)
Male
Gametophyte
(n)
Sperm
(n)
Seed plants
Layers of integuments
envelope and protect the
megasporangium
In this example we
are using a pine cone
Integument
A megaspore
develops into a
multicellular
female
gametophyte
Spore wall
Megasporangium
(2n)
Megaspore
(n)
The whole structure –
megasporangium, megaspore, and
integuments – is called an ovule
Unfertilized ovule
Fig. 30.3
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
Seed plants
Compared to a
single-celled
spore, a seed is
much more
resistant and
complex
Fertilization initiates the
transformation of the ovule into a
seed
Seed coat
(derived from
Integument)
Food supply
Embryo (2n)
(new sporophyte)
Fig. 30.3
Gymnosperms
“Naked seeds”;
not enclosed by
an ovary and
develop on the
surface of
modified leaves
that usually form
cones (strobili)
Gymnosperms
Phylum
Ginkgophyta
Ginkgo biloba is
the only living
species of this
entire phylum
Gymnosperms
Phylum
Cycadophyta
(cycads, sago
palms)
Thrived during the
“Age of
Dinosaurs”; only
~130 species
alive today
Gymnosperms
Phylum
Cycadophyta
(cycads, sago
palms)
Thrived during the
“Age of
Dinosaurs”; only
~130 species
alive today
♀
♂
Gymnosperms
Phylum
Gnetophyta
3 genera:
Gnetum
Gymnosperms
Phylum
Gnetophyta
3 genera:
Gnetum
Ephedra
Gymnosperms
Phylum
Gnetophyta
3 genera:
Gnetum
Ephedra
Welwitschia
Gymnosperms
Phylum
Coniferophyta
E.g., longleaf
pine
Gymnosperms
Phylum
Coniferophyta
E.g., longleaf
pine, giant
sequoia
Gymnosperms
Phylum
Coniferophyta
E.g., longleaf
pine, giant
sequoia, cypress
Gymnosperms
Phylum
Coniferophyta
E.g., longleaf
pine, sequoia,
cypress, and ~600
other conebearing species
Gymnosperms
(e.g., pine)
Key
Sporophyte
Megasporangia and
microsporangia are
found in separate
cones
Haploid
Diploid
Ovulate
cone
Megasporangium
Gametophytes
Pollen
cone
Megasporocyte
Meiosis
Meiosis
Meiosis produces
spores and begins
the haploid generation
Microsporocyte
Microsporangium
Egg
Megasporocytes (2n) are the cells within megasporangia
that
undergo meiosis to produce megaspores (n)
Microsporocytes (2n) are the cells within microsporangia
that undergo meiosis to produce microspores (n)
Fertilization
Fig. 30.6
Gymnosperms
(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulate
cone
Megasporangium
Gametophytes
Pollen
cone
Megasporocyte
Meiosis
Each megaspore develops
into a female gametophyte
Meiosis
Microsporocyte
Microsporangium
Pollen
Megaspore
Each microspore develops
into a male gametophyte (a
pollen grain)
Egg
A pollen grain gains access to
a female gametophyte through
a micropyle
Fertilization
Fig. 30.6
Gymnosperms
(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulate
cone
Megasporangium
Gametophytes
Pollen
cone
Megasporocyte
Meiosis
The female gametophyte
contains 2 or 3 archegonia,
each with 1 egg cell
Meiosis
Microsporocyte
Microsporangium
Pollen
Megaspore
Two cells of the male
gametophyte are sperm
Archegonium
Egg nuclei
Sperm nuclei
Fertilization
Fig. 30.6
Gymnosperms
(e.g., pine)
Fertilization (union
of 1 egg and 1
sperm) produces an
embryo
Key
Sporophyte
Haploid
Diploid
Ovulate
cone
Megasporangium
Gametophytes
Pollen
cone
Megasporocyte
Meiosis
Meiosis
Microsporocyte
Microsporangium
Pollen
Megaspore
Archegonium
Egg nuclei
Embryo
Sperm nuclei
Fertilization
Fig. 30.6
Gymnosperms
(e.g., pine)
Key
Sporophyte
Haploid
Diploid
Ovulate
cone
Fertilization (union
of 1 egg and 1
sperm) produces an
embryo
Megasporangium
Gametophytes
Pollen
cone
Megasporocyte
Meiosis
Meiosis
Embryos develop
within seeds
Microsporocyte
Microsporangium
Seedling
Pollen
Seeds germinate
and embryos
become seedlings
Megaspore
Archegonium
Seed
Egg nuclei
Embryo
Sperm nuclei
Fertilization
Fig. 30.6
Plant Origins
Land plants
Flowering plants
(Angiosperms) –
the other surviving
lineage – appeared
~200 million years
later
Vascular plants
Angiosperms
Seed plants
Gymnosperms
Pterophyte
(ferns, horsetails, whisk fern)
Seedless vascular plants
Lycophytes
(club mosses etc.)
Mosses
Hornworts
Liverworts
Seed plants
appeared ~360
m.y.a. with the rise
of the
Gymnosperms
Charophyceans
Bryophytes
(nonvascular plants)
Origin of seed plants
(about 360 mya)
Origin of vascular
plants (about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
Hashed lines indicate uncertainties
Fig. 29.7
Angiosperms
Flowering plants;
seeds develop inside
sporophyte ovaries
Angiosperms
BASAL ANGIOSPERMS
Flowering plants;
seeds develop inside
sporophyte ovaries
Amborella trichopoda
Star anise
6 main clades
(see pg. 602)
Magnolia grandiflora
Eudicots
Monocots
Magnoliids
Star anise
Water lilies
HYPOTHETICAL TREE OF FLOWERING PLANTS
Amborella
~250,000 extant species
Water lily
Angiosperms
(a.k.a., flowering
plants)
Carpel
(♀)
Stigma
Style
Ovary
Petal
Anther
Filament
Stamen (♂)
Sepal
Ovule
Receptacle
Fig. 30.7
Angiosperms
Complete flowers have sepals, petals,
stamens & carpels
See Fig. 30.7
Angiosperms
Complete flowers have sepals, petals,
stamens & carpels
See Fig. 30.7
Angiosperms
Complete flowers have sepals, petals,
stamens & carpels
See Fig. 30.7
Angiosperms
Complete flowers have sepals, petals,
stamens & carpels
Ovules
See Fig. 30.7
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
Angiosperms
Incomplete flowers lack one or more of the following:
sepals, petals, stamens or carpels
E.g., most grasses lack petals
Angiosperms
Self-fertilization
Some bisexual flowers
can self-fertilize
See Fig. 30.7
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
Angiosperms
Dioecious species have separate male and female
individuals; which eliminates the possibility of selffertilization
Staminate
flowers
Carpellate
flowers
E.g., branches from two holly plants
Angiosperms
Monocots
Eudicots
1 cotyledon
2 cotyledons
Parallel
veins
Netlike
veins
Scattered
vascular tissue
Ring of
v. tissue
Fibrous roots
Tap root
1 opening
in pollen
See Fig. 30.12
3 openings
in pollen
Floral organs Floral organs
in 4s or 5s
in 3s
Angiosperms
Key
Haploid
Diploid
Microsporangium
Anthers contain
microsporangia that
produce microspores
Each microspore
forms a pollen grain
(a male
gametophyte)
Ovules contain
megasporangia that
produce megaspores
Microspore
Meiosis
Pollen
Sporophyte
Meiosis
Megasporangium
Gametophytes
Megaspore
Embryo sac
Each megaspore
forms an embryo sac
(a female
gametophyte)
Fertilization
Fig. 30.10
Angiosperms
Key
Haploid
Diploid
Microsporangium
Pollen disperses to
stigmas
Double fertilization is
unique to
angiosperms
Microspore
Meiosis
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;
the second sperm
unites with 2 nuclei
of the embryo sac to
produce triploid (3n)
endosperm
Embryo
Embryo sac
Egg
Zygote
2 sperm
Fertilization
Endosperm
Fig. 30.10
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)
Spores (1n)
Gametes (1n)
Gametophyte (1n)
(If bryophyte, seedless vascular or gymnosperm,
archegonia & antheridia present)
Seed plants and human welfare
Humans began practicing agriculture only
about 18,000 years ago
Multiple independent origins
Seed plants and human welfare
Even so, most of our food currently
comes from angiosperms
Just 6 crops – wheat, rice, maize (corn), potatoes,
cassava (manioc), sweet potatoes – yield 80% of all the
calories consumed by humans
Seed plants and human welfare
It takes ~5 pounds of grain to produce
1 pound of grain-fed beef