Transcript Overview of Plant Evolution

Four main groups of Land Plants
 Bryophytes
(mosses, etc.)
 Ferns and relatives
 Gymnosperms
 Angiosperms
Bryophytes
 There



are three groups of bryophytes
Mosses 12,000 species
Liverworts 6,500 species
Hornworts 100 species
Bryophyte diversity
Hornworts
100 species
Liverworts
6,500 species
Mosses
12,000 species
Mosses
Mosses 12,000
species
Widely distributed, especially in alpine, boreal,
temperate, and tropical forests
Able to live in very dry or very cold habitats
Many can dry out entirely, then rehydrate
Famous mosses:
Sphagnum
Wetland moss “peat moss”
Boggy regions
dominated by it known
as peat bogs or
peatlands
Liverworts and hornworts

Liverworts are even less conspicuous than
mosses. Some have a lobed appearance.
 They reproduce both sexually and asexually
from small bundles of cells known as gemmae.

Hornworts have elongated sporophytes that are
hornlike in appearance. They are unusual in
that each photosynthetic cell contains one large
chloroplast rather than many smaller ones.
Bryophytes
 Bryophytes
arose at least 400 mya and
possess two adaptations that allow them
to survive on land.


Waxy cuticle reduces water loss
Gametes are protected and develop within
gametangia.
Bryophytes
 Bryophytes
do not have a vascular system
and so cannot grow very large.
 They
also need moisture to reproduce
because fertilization depends on sperm
being able to swim through water to reach
the egg.
 In
bryophytes the gametophyte
(haploid n) is the dominant
generation and the sporophyte
(diploid 2n) is dependent on the
gametophyte.
Bryophytes
Gametophytes only a few
cells thick. No true “leaves”.
Directly absorb water &
minerals.
No lignified vascular tissue.
Bryophyte gametophyte
Close to the ground.
Anchored by rhizoids.
Long, tubular single cells - not
tissues.
Bryophyte
sporophyte
3) Capsule
3 parts
2) Stalk
1) Basal foot
Bryophyte life cycle
sporophyte
meiosis
spores
2n
n
embryo
gametophyte
zygote
eggs
sperm
Bryophyte reproduction
Spores produced in
capsule (sporangium)
Spores released to germinate into gametophytes.
Bryophyte reproduction
 Male
gametophytes produce sperm and
female gametophytes produce eggs.
 When
there is sufficient moisture sperm
swim to the egg and fertilize it. Fertilized
egg develops into a zygote and ultimately
into a sporophyte.
Seedless vascular plants: Ferns
and fern allies
 First
vascular plants originated about 420
mya.
 First seed plants came later about 360
mya.
 Seedless vascular plants dominated the
planet during the Carboniferous period
(300-350 mya).
Seedless vascular plants: Ferns
and fern allies
 Giant
tree ferns, horsetails and lycopods
were the dominant vegetation of the
Carboniferous period.
 Their
fossilized remains formed extensive
coal beds.
 They
were ultimately superseded by the
seed plants and far fewer survive today.
Present day fern allies
 Lycopods: About
1,000 species. Includes
tropical epiphytes and northern
hemisphere low growing club mosses.
 Horsetails:
today about 15 species of
Equisetum occur in northern hemisphere
in damp conditions.
Equisetum
Lycopod
Ferns
 A very
diverse group about 12,000 species
most abundant in the tropics, but
distributed worldwide.
 Most
are small to moderately large plants,
but tree ferns are many meters tall.
Common ferns
Boston fern
Staghorn fern
Maidenhair fern
Pteris
Fern morphology
Dominant generation: sporophyte
Fern morphology
Body consists of three organs:
• Underground rhizome (stem)
• Adventitious roots
• Fronds (leaves)
Fern morphology
• Underground rhizome (stem)
Fern morphology
• Adventitious roots
Roots that grow from
anywhere but the
primary root.
Like out of stems.
Fern morphology
• Fronds (leaves)
“fiddlehead”
Fern life cycle
Independent and
dominant sporophyte
2n
meiosis
spores
n
embryo
Free-living gametophyte
zygote
eggs
sperm
Fern life cycle
Fern life cycle - spores
Unit of dispersal = spores
• Produced by sporangia
• Sporangia clustered in sori
(singular = sorus)
• Usually small button-like
dots on backs of fronds
Fern life cycle - sori
Fern life cycle - sori
Fern morphology
Free-living gametophyte
• Also called a prothallus
• Produces sperm and eggs
• Sporophyte starts attached to
gametophyte. Gametophyte
dies after sporophyte
detaches.
Sporophyte
Spores and seeds
 The
spores of ferns are tiny and vast
numbers are produced. However, their
prospects of survival are low.
 A new
evolutionary innovation, the seed,
arose in the Carboniferous Period. Seeds
and later fruit proved to be enormously
successful and seed plants especially
angiosperms came to dominate the planet.