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Dr. Mitch Pavao-Zuckerman
Department of Ecology and Evolutionary Biology
621-8220
[email protected]
Office hours: Biosciences West 431
W and F 1-2 p.m. or by appointment
Diversity of Plants
Diversity of Plants (Fig 29.4)
Ancestral Alga
Chlorophyta
Nontracheophytes
Nonseed Tracheophytes
Gymnosperms
The Transition to Life on
Land
The Vascular Plants
The Seed Plants
The Flowering Plants
Angiosperms
Monophyly
• Monophyletic group – includes the
most recent common ancestor and all
decendents
• These are NOT monophyletic:
Green Plants
(viridiphytes) are a
monophyletic group
• Green Plants include the
Chlorophytes (green algae)
• Other green algae
• and the land plants
Embryophytes (Land Plants)
Land Plants are also a monophyletic group
• Photosynthetic eukaryotes that use
chlorophyll a and b and store
carbohydrates starch
• Resting embryo with placental connection to
the parent.
The Conquest of the Land
History of plants on land
• 500 mya - a few algae and lichens.
• By 460 mya - primitive Land Plants,
• By 425 mya - Early Vascular Plants
were common
• How did it happen?
• Obstacles?
Reconstruction
Fossil
The Conquest of the Land
Early innovations in land plant
evolution:
1. cuticle (waxy coating)
2. thick spore wall
3. Antheridia and archegonia
(gamete cases),
4. protected embryo
5. protective pigments – flavonoids
absorb damaging UV light
Land Plants (Embryophytes) (Fig 29.4)
Ancestral Alga
Protected
Embryos
Chlorophyta
Nontracheophytes
Nonseed Tracheophytes
Gymnosperms
Plant Kingdom?
Angiosperms
Nontracheophytes:
Liverworts, Hornworts, and Mosses
• Small plants (compared to present day
shrubs and trees)
• Lack specialized water (xylem) and food
conducting tubes (phloem) of vascular
plants.
• Rely on diffusion of water and minerals.
Plant life cycles feature alternation of
generations (Fig 29.2)
Haploid
Multicellular
gametophyte
Gametes
Spore
Meiosis
Haploid (n)
Fertilization
Diploid (2n)
Zygote
Multicellular
sporophyte
Diploid
Nontracheophytes:
Liverworts, Hornworts, and Mosses
• Diploid generation is
smaller than the
haploid generation
and
• Diploid depends on it
for water and nutrition.
• “The big green thing”
is the haploid stage.
• The diploid stage is
attached to it.
Fig. 29.5
Liverworts
(9,000 species)
• Lack stomates (pores with guard
cells that regulate C02 uptake and
H20 loss).
• Small spore producing diploid phase
compared to hornworts or mosses
Hornworts
(100 species)
• Have stomates
• Horn-shaped spore producing
diploid stage
• One large flat chloroplast per cell
Mosses
(15,000 species)
• Have stomates
• Spore producing upright diploid
stage with capsule
• Capsule has a lid and row of teeth
that release the spores in wet
weather.
What is not a common feature of non-vascular plants?
a. They are all relatively small
b. They all lack specialized conductive tissue such as
xylem and phloem
c. All possess stomata for gas exchange
d. The big generation is haploid (one set of chromosomes)
with the smaller diploid (two sets of chromosomes)
generation attached and dependent.
Land Plants (Embryophytes) (Fig 29.4)
Ancestral Alga
Protected
Embryos
Vascular tissue
Vascular Plants
Chlorophyta
Nontracheophytes
Nonseed Tracheophytes
Gymnosperms
(Tracheophytes)
Angiosperms
Vascular Plants
• Thick-walled dead water-conducting
cells.
‹ more efficient water movement
‹ support for tall plants.
Vascular Plants
• The diploid generation became
independent of the haploid generation.
LARGER and
Figure
28.19
Figure 29.20
Tracheophytes
• The earliest
tracheophytes lacked
roots.
• Roots – possibly
evolved from branches
Tracheophytes
• Simple leaves may have
evolved from the spore
producing structures.
• Complex leaves may have
evolved from a branching
stem system.
Difference?
Land Plants (Embryophytes) (Fig 29.4)
Ancestral Alga
Protected
Embryos
Vascular tissue
Vascular Plants
Chlorophyta
Nontracheophytes
Nonseed Tracheophytes
Gymnosperms
(Tracheophytes)
Angiosperms
Nonseed Tracheophytes
Club mosses 1,200 species
•
•
•
Simple leaves
Cone-like structures with spores.
Dominated tropical coastal swamps in
Carboniferous period 300 myaÆ coal
deposits.
• Selaginella is common here in the desert.
Nonseed Tracheophytes
Whisk Ferns 15 species
•
•
•
Simple branching like ancient vascular plants.
Tiny simple leaves
Reconstruction of ancient
No true roots
tracheophyte
Tracheophytes
Horsetails 15 species
•
•
•
•
Jointed hollow stems
Silica deposits (“scouring rush”)
Leaves in whorls
Spore sacs under “shields” on
“cones”
Nonseed Tracheophytes
Ferns 12,000 species
• Big complex leaves with branching veins
• Spores in sacs clustered on the bottom of
•Tree ferns can reach 60 ft
the leaf
• Leaves unfold from “fiddlehead”
What is not a common feature of Non-Seed Tracheophytes?
a. They are larger than non-vascular plants
b. They possess specialized cells for moving water and
food
c. All possess stomata for gas exchange
d. The big generation is haploid (the gametophyte with
one set of chromosomes)
Land Plants (Embryophytes) (Fig 29.4)
Ancestral Alga
Chlorophyta
Nontracheophytes
Protected
Embryos
Vascular tissue
Seeds
Seed plants
Nonseed Tracheophytes
Gymnosperms
Angiosperms
Seed Plants
300,000 species
• The seed plants have greatly reduced
haploid stage.
• How did this happen?
Fig 30.2
Seed Plants
300,000 species
• Further reduced haploid generation.
‹
Part of the evolution of seeds
and pollen.
• Seeds - protected resting stage
opening many possibilities, like
suspended animation.
•Pollen - sperm delivery system;
escape the need of water for
sperm to swim.
How did seeds evolve?
• Ancestors of seed plants had one kind of spore.
• First dimorphic spores evolved:
‹ Microspores (grow into sperm producing haploid stage)
‹ Megaspores (grow into egg producing haploid stage)
• Megaspores reduced to just one.
Spore sac
How did seeds evolve?
• Megaspore enveloped in a sac.
• Female haploid stage grows in this “seed”.
• It is attached to the diploid parent.
Pollen is a reduced male haploid stage
Plant and flower are diploid
Diploid
Spore sac
Reduced
haploid
stage
Haploid
Spores
Pollination
1.
2.
3.
Pollen Æ reduced haploid female.
Pollen produce sperm to fertilize an egg.
The zygote develops into a seed embryo.
Seed Plants
300,000 species
• So, seed plants make seeds and
pollen
• Also make wood.
• Evolved ~ 370 mya
Land Plants (Embryophytes) (Fig 29.4)
Ancestral Alga
Chlorophyta
Nontracheophytes
Protected
Embryos
Vascular tissue
Seeds
Nonseed Tracheophytes
Gymnosperms
Angiosperms
Seed Plants - Gymnosperms
• Gymnosperm = ‘naked seeded’
• Do not have flowers or fruit tissue
Gymnosperms - 4 Phyla
Cycads
Gnetophytes
Ginkos
Gymnosperms - Conifers
• Leaves often “evergreen” needles
or scales
• Cones: scales with seeds
Seed Plants- Conifers
• Longest-lived trees - Bristlecone
pine: 5,000y
• Tallest tree – redwood 112 m
• Most massive tree – sequoia – 11m
wide
Land Plants (Embryophytes) (Fig 29.4)
Chlorophyta
Ancestral Alga
Nontracheophytes
Protected
Embryos
Nonseed Tracheophytes
Vascular tissue
Seeds
Gymnosperms
Flowers
Flowering Plants
Angiosperms
Seed Plants - Angiosperms
•
•
Highly diverse plant phylum
Dominant form of plant life on Earth
• Because of differences from other plants
Seed Plants - Angiosperms
Pollination
• Pollen lands on stigma, rather than at the
tip of the ovule
• Reduces chance of self-pollination –
increases genetic diversity
Fig 30.7, 30.11
Double fertilization (producing zygote and
endosperm)
• Flowers and fruit are unique features
Endosperm
Nucleus
Seed Plants Angiosperms
• Fruit and stamens
evolved from leaf-like
structures.
Seed Plants - Angiosperms
• Much diversity is related to pollination and
dispersal mechanisms.
Seed Plants Angiosperms
Review Land Plants (Fig 29.4)
Chlorophyta
Ancestral Alga
Nontracheophytes
Protected
Embryos
Nonseed Tracheophytes
Vascular tissue
Seeds
Plant Kingdom?
Tracheophytes?
Seed plants?
Gymnosperms
Flowers
Angiosperms