Plant Evolution &
Diversity – Ch. 22-25
Kingdom Protista: Algae & Protozoa
• Organisms in this Kingdom don’t fit clearly into
what we call plant, animal, or fungi.
• Most diverse eukaryotic Kingdom (>60,000
species).
• We are interested in this Kingdom because of the
Chlorophytes & Charophyceans - green algae.
The line between Kingdom Protista and Kingdom
Plantae is still being discussed……
Fig 29.4
Origin
of
Plants
Characteristics of Green Algae - Chlorophytes
• There are unicellular and multicellular forms
• Can live symbiotically with fungi as lichens
Fig 28.30
Volvox - freshwater
Ulva – sea lettuce
Caulerpa - intertidal
Characteristics of Green Algae - Charophyceans
•
•
fresh water ponds
They are considered to be the closest ancestors of
true plants. Evidence:
1. .
2. .
3. .
4. Both form a cell plate during cell division
5. Genetic evidence – charophyceans share a greater
% of similar DNA with true plants than any other
algae
Plants
• So how are they different from
Charophyceans??
What challenges did plants face when
they “moved” onto land?
Adaptation to life on Land:
1. .
2. .
3. .
4. Multicellular gametangia
5. Multicellular, dependent embryos
1. Apical Meristems –
2. Alternation of Generations
•
2 multicellular life stages:
1. Sporophyte:
• Diploid
• Divides by meiosis to form spores
• Spores – haploid cells that can grow into a
new, multicellular, haploid organism (the
gametophyte) without fusing to another cell.
2. Gametophyte:
• Haploid
• Divides by mitosis to form the gametes (egg
and sperm)
• Egg & sperm fuse to form the diploid zygote,
which divides by mitosis to form the sporophyte
3. Walled spores produced in sporangia
• Sporopollenin protects the spore from harsh
environmental conditions
• Sporangia =
• Sporocytes = the diploid cells within the sporangia
that divide by meiosis to form the haploid spores
sporocytes
4. Multicellular gametangia
•
•
Gametangia =
2 types of gametangia:
1. Archegonia –
2. Antheridia –
• Sperm travel to the egg, fertilizing it within the
archegonia.
5. Multicelluar, dependent embryos
• Zygote divides by mitosis to become the
sporophyte.
Other examples of adaptations to life on land:
(not all plants have the following):
1. Cuticle –
2. Secondary compounds –
3. Roots –
4. Shoots - stems and leaves to make food.
5. Stomata – openings in the leaf surface to allow gas
exchange for photosynthesis and to regulate water loss.
More Adaptations
4. .
5. A vascular system that transports food & water
from roots to shoots and vice versa.
Fig 29.7
Nonvascular Land Plants: Bryophytes
•
•
Earliest land plants
3 Phyla:
1. Hepatophyta –
2. Anthocerophyta –
3. Bryophyta • .
•
•
Peat moss (sphagnum): doesn’t decay rapidly,
stores 400 bil tons of carbon
Gametophyte is the dominant generation:
Moss
life
cycle
Fig 29.8
Phylum Hepatophyta – liverworts
Phylum Anthocerophyta – hornworts
Phylum bryophyta - mosses
Peat bogs –
sphagnum
moss
Fig 29.10
Vascular Plants
• Vascular tissue:
– Xylem = water & mineral transport
– Phloem = food (carbohydrates) transport
• .
• Sporophytes branched, independent of
gametophyte parent
Seedless Vascular Land Plants
-Egg & sperm need moist environment to fertilize
(similar to bryophytes)
Two phyla of seedless vascular plants:
1. Phylum Lycophyta (Club Mosses)
- flammable spore clouds
- were tree-like in the Carboniferous period
Phylum Lycophyta: clubmosses,
spikemosses, quillwarts
2. Phylum Pterophyta
a) Whisk ferns –
b) Horsetails –
c) Ferns – produce clusters (sori) of sporangia on
underside of leaves (fronds)
Phylum Pterophyta: ferns, horsetails, whisk ferns
Fig 29.12 Life cycle of a fern
Forests of the Carboniferous period (290-360
mil years ago):
• Heat + pressure + time ----> coal
• Pulled lots of CO2 out of atmosphere, cooling the
earth & forming glaciers
• Larger species died out when climate became drier
Terrestrial Adaptations of Seed Plants
1. Seeds replace spores as main means of dispersal.
• Why?
2. Gametophytes became reduced and retained
within reproductive tissue of the sporophyte
3. Heterospory –
4. Zygote develops into an embryo packaged with
a food supply within a protective seed coat.
5. Pollen & Pollination - freed plants from the
requirement of water for fertilization.
1. Seeds replace spores as main means of dispersal.
• old way (ferns & mosses) =
• new way: the sporophyte RETAINS its spores
within the sporangia & the tiny gametophyte
develops within the spore.
• ovule =
• after fertilization, the ovule becomes the seed
• seed = sporophyte embryo + food supply (mature
ovule tissues)
2. Reduction of the gametophyte:
Similar to Fig 30.2
3. Heterospory – separate male & female
gametophytes
• Old way: sporangia  spores  bisexual
gametophyte (antheridia  sperm, archegonia ->
eggs)
• New way:
• Microsporangia  microspores  male
gametophyte  sperm
4. Ovules and seed production
• Megasporangia protected by layers of tissue called
integuments.
• Ovule =
• After fertilization, embryo develops, ovule
becomes a seed
Fig 30.3
5. Pollen & Pollination
• Microsporangia  microspores  male
gametophyte  sperm
• Pollen =
• Pollination =
• Pollen tube brings sperm to egg within the ovule
Two types of seed plants:
1. Gymnosperms
•Evolved first
•“naked seed” –
•
2. Angiosperms
•Evolved from gymnosperms: Sporophylls
rolled together to form ovaries.
Gymnosperms
•
Four phyla:
1. Ginkophyta –
2. Cycadophyta –
3. Gnetophyta –
4. Coniferophyta –
 Dominate forests of the N. hemisphere
 Most are evergreen
 Needle-shaped leaves to reduce water loss
during drought
Phylum Cycadophyta
Phylum Ginkophyta
Phylum Gnetophyta
Phylum
Coniferophyta
Fig 30.6
Angiosperms
•
One phylum: Anthophyta
•
Formerly only 2 classes: monocots & dicots. Now 4
clades (evolutionary lines):
1.
2.
3.
4.
Basal angiosperms
Magnoliads
Monocots
Eudicots
Evolutionary success of Angiosperms
due to:
1. .
2. Flowers – attract pollinators
3. Fruits – many forms for variety of dispersal
mechanisms
Fig 30.3
Notice the triploid stage!
•Each pollen grain (male gametophyte) produces two
sperm
•Sperm travel down the pollen tube & into the ovule.
•Double fertilization –
•Ovule matures into the seed – contains sporophyte
embryo & endosperm (food).
•Ovary (female sporangium tissues) matures into the
fruit.
Kingdom Fungi (A tiny bit of Ch. 21)
But Fungi:
• their bodies are filamentous
• the organization of large structures such as
mushrooms and morels is completely different from plants,
• they are heterotrophs (aquire nutrients by absorption)
• Hence the boot!!
Ecological Roles of Fungi:
1. Decomposers –
Ecological Roles of Fungi:
2. Parasites – absorb nutrients from living hosts.
Ecological Roles of Fungi:
3. Mutualists with plants –
. ex. mycorrhizae
•Lichens: symbiotic association of cyanobacteria or
green algae and fungi.
–Lichens are very sensitive to air pollution; used
as indicators of air quality.
Lifestyles of Fungi, continued
• Mycorrhizae: mutualistic association of plant roots
and fungi.
– Fungus receives food from the root exudates.