Plant Evolution & Diversity
I. Kingdom Protista: Algae & Protozoa
A. Characteristics
1. Simple Eukaryotes – mostly single-celled Amoeba, slime
molds, euglenoids, algae
2. Organisms in this Kingdom don’t fit clearly into what we
call plant, animal, or fungi.
3. Most diverse eukaryotic Kingdom (>60,000 species).
4. 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
II. Plant Origins
A. Suspects and Evidence
1. Characteristics of Green Algae - Chlorophytes
a. Mostly freshwater, but some are marine.
b. Have plant-like chloroplasts.
c. There are unicellular and multicellular forms
d. Can live symbiotically with fungi as lichens
Fig 28.30
Volvox - freshwater
Ulva – sea lettuce
Caulerpa - intertidal
2. Characteristics of Green Algae - Charophyceans
a. fresh water ponds
b. They are considered to be the closest ancestors of
true plants. Evidence:
i. Both have same type of cellulose-synthesizing
complexes in cell membrane
ii. Both have peroxisomes for enzyme storage
iii. Both have same type of flagellated sperm
iv. Both form a cell plate during cell division
v. Genetic evidence – charophyceans share a
greater % of similar DNA with true plants than any
other algae
III. Plants Shared Characteristics
A. Plants are multicellular eukaryotes that are
photosynthetic autotrophs.
B. Shared pigments
C. Cellulose cell walls
D. Store glucose as starch
E. Etc.
IV. What challenges did plants face when
they “moved” onto land?
A. Issues Faced
1. Acquire, transport, and conserve water
2. Protect from UV radiation
3. Resist pathogens (bacteria) and herbivores
(later)
4. Others?
Then why move onto land?
B. Advantages
1.
2.
3.
4.
C. Adaptation to life on Land:
1. Apical Meristems
3. Walled spores produced in sporangia
5. Multicellular, dependent embryos
4. Multicellular gametangia
2. Alternation of generations
1. Apical Meristems – localized regions of cell division
at tips of roots and shoots
Fig 29.5
2. Alternation of Generations
Fig 29.5
a. 2 multicellular life stages:
i. 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.
ii. Gametophyte:
* Haploid
* Divides by mitosis to form the gametes (egg
and sperm)
b. Egg & sperm fuse to form the diploid zygote, which
divides by mitosis to form the sporophyte
3. Walled spores produced in sporangia
a. Sporopollenin protects the spore from harsh
environmental conditions
b. Sporangia = an organ within the sporophyte that
produces the spores
c. Sporocytes = the diploid cells within the sporangia
that divide by meiosis to form the haploid spores
sporocytes
Fig 29.5
4. Multicellular gametangia
a. Gametangia = multicellular organs within the
gametophyte that produce the gametes by mitosis.
b. 2 types of gametangia:
i. Archegonia – produce eggs
ii. Antheridia – produce sperm
c. Sperm travel to the egg, fertilizing it within the
archegonia.
Fig 29.5
5. Multicelled dependent embryos
a. After fertilization, the zygote remains
within the archegonia, gaining nutrients for
growth from the gametophyte.
b. Zygote divides by mitosis to become the
sporophyte.
6. Other examples of adaptations to life on land:
(not all plants have the following):
a. Cuticle – waxy covering to prevent desiccation &
microbial attack
b. Secondary compounds – odors, toxins, tastes, etc. to
attract pollinators and defend against herbivores
c. Roots - absorb water and minerals from the soil
d. Shoots - stems and leaves to make food.
e. Stomata – openings in the leaf surface to allow gas
exchange for photosynthesis and to regulate water loss.
f. Lignin in cell walls to provide structural support for
Shoots
g. A vascular system that transports food & water from
roots to shoots and vice versa.
V. Plant Phyla
Common Name # of Species
Nonvascular Plants
Bryophyta
Hepatophyta
Anthocerophyta
Mosses
Liverworts
Hornworts
10,000
6,500
100
Vascular Seedless Plants
Psilophyta
Lycophyta
Sphenophyta
Pterophyta
Whisky ferns
Club mosses
Horsetails
Ferns
10 - 13
1,000
15
12,000
Vascular Seed Plants
Coniferophyta
Cycadophyta
Ginkgophyta
Gnetophyta
Anthophyta
Conifers
Cycads
Ginkgo
Gnetae
Flowering plants
550
100
1
70
250,000
Table 1 Classification of Plants at the level of Phylum This table shows
the major plant phyla that are used today.
Fig 29.7
A. Nonvascular Land Plants: Bryophyta
1. Characteristics
a. Earliest land plants
b. Phyla: Hepatophyta – liverworts,
Anthocerophyta – hornworts, and Bryophyta –
mosses
c. Inhabit most environments, including extremes
d. Peat moss (Sphagnum): doesn’t decay rapidly,
stores 400 billion tons of carbon
e. Gametophyte is the dominant generation
f. No true roots nor leaves
2. Moss Life Cycle
Fig 29.8
3. Bryophyta Phyla
a. Hepatophyta – liverworts
b. Anthocerophyta – hornworts
c. Bryophyta - mosses
d. Sphagnum moss (stores carbon, doesn’t decay, fuel
source) Peat bogs
Fig 29.10
B. Vascular Plants
1. Characteristics
a. Vascular tissue  Xylem = water & mineral
transport and Phloem = food (carbohydrates) transport
b. Dominant generation = sporophyte
c. Sporophytes branched, independent of gametophyte
parent
d. Leaves = Microphylls to Megaphylls
e. Root development
2. Groups
a. Seedless Vascular Plants
i. Characteristics
Tiny gametophytes living just above or below soil surface
Egg & Sperm need moist environment to fertilize (similar to
bryophytes)
Microphyll leaves
b. Two phyla of seedless vascular plants:
i. Phylum Lycophyta (Club Mosses)
They diverged first from bryophytes with an unbranched
vascular system, flammable spore clouds, and were tree-like
in the Carboniferous (late Paleozoic) period
ii. Phylum Pterophyta
Whisk ferns – no true leaves or roots
Horsetails – hollow air-filled stems (adaptation to water-logged,
low O2 environment)
Ferns – produce clusters (sori) of sporangia on underside of
leaves (fronds)
Phylum Lycophyta: club mosses, spike
mosses, quill warts
Phylum Pterophyta: ferns, horsetails, whisk ferns
c. Fern Life Cycle
Fig 29.12
d. Factors  forest changes of the Carboniferous
period (290 to 360 mya)
i. Lycophytes (tree-like) & Pteridophytes
ii. First forests
iii. Swampy forests – slow decay in low O2, formed deep
layers of organic matter
iv. Heat + pressure + time => coal
v. Pulled lots of CO2 out of atmosphere, cooling the
earth & forming glaciers
vi. Larger species died out when climate became drier
3. Terrestrial Adaptations of Seed Plants
a. Seeds replace spores as main means of dispersal.
i. Why?
ii. More resistant to harsh environ b/c multicellular
iii. old way (ferns & mosses): spores released from
sporangia to disperse and develop into gametophytes
iv. new way: the sporophyte RETAINS its spores
within the sporangia & the tiny gametophyte
develops within the spore.
v. ovule = female sporangium + female spore.
Female gametophyte develops within the spore &
produces eggs.
vi. after fertilization, the ovule becomes the seed
vii. seed = sporophyte embryo + food supply (mature
ovule tissues)
b. Reduction of the gametophyte:
Similar to Fig 30.2
c. Heterospory – separate male & female
gametophytes
i. Old way: sporangia  spores  bisexual gametophyte
(antheridia  sperm, archegonia  eggs)
ii. New way:
Megasporangia  megaspores  female gametophyte 
eggs
Microsporangia  microspores  male gametophyte 
sperm
d. Ovules and seed production
i. Megasporangia protected by layers of tissue called
integuments.
ii. Ovule = integuments, megasporangia, & megaspore
iii. Megaspore  female gametophyte  egg & food
supply
iv. After fertilization, embryo develops, ovule becomes
a seed
Fig 30.3
e. Pollen & Pollination
i. Microsporangia  microspores  male
gametophyte  sperm
ii. Pollen = male gametophyte
iii. Pollination = transfer of pollen to ovule by wind
or animals
iv. Pollen tube brings sperm to egg within the ovule
4. Two types of seed plants:
a. Gymnosperms
i. Characteristics
Evolved first and “Naked seed” – seeds
develop on surface of specialized leaves called
sporophylls
ii. Four phyla:
Ginkophyta – only Ginko biloba
Cycadophyta – Cycads (look like palms)
Gnetophyta – Gnetophytes (tropical trees)
Coniferophyta – Conifers – cone-bearing trees
Dominate forests of the N. hemisphere
Most are evergreen
Needle-shaped Megaphyll leaves to reduce water
loss during drought
Phylum Cycadophyta
Phylum Ginkophyta
Phylum Gnetophyta
Phylum Coniferophyta
Fig 30.6
iii. Gymnosperm Life Cycle
b. Angiosperms
i. Characteristics
Flowering plants, Most diverse, and Evolved from
gymnosperms: Sporophylls rolled together to form
ovaries.
ii. One phylum: Anthophyta
Seeds are enclosed in the moist reproductive tissue of the
sporophyte generation (Ovary).
More insects and animals for pollination, less dependent
on wind.
Formerly only 2 classes: monocots & dicots. Now 4
clades (evolutionary lines): Basal angiosperms (Liliopsida),
Magnoliopsida, Monocots, & Eudicots
iii. Evolutionary success of Angiosperms
Increased water transport efficiency due to
improvement in xylem tissue: tracheid cells, fiber
cells, vessel elements (gymnosperms only have
tracheids)
Flowers – attract pollinators
Fruits – many forms for variety of dispersal
mechanisms
iv. Angiosperm Life Cycle
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 – one sperm unites with the egg to
form the 2n zygote, other sperm unites with the two
nuclei of the female gametophyte to form a 3n
endosperm – becomes food for the developing embryo
Ovule matures into the seed – contains sporophyte
embryo & endosperm (food).
Ovary (female sporangium tissues) matures into the
fruit.
Moss Life Cycle
Fig 29.8
Fern Life Cycle
Fig 29.12
Fig 30.6
Gymnosperm Life Cycle
Angiosperm Life Cycle
Fig 30.3
VI. Kingdom Fungi
Fungi were once included in the plant kingdom because
they produce spores, have cell walls, and are not
animals.
A. Characteristics
1. Their cell walls do not contain cellulose (like plants),
but do contain chitin (like insects, arthropods).
2. Their bodies are filamentous.
3. The organization of large structures such as
mushrooms and morels is completely different from plants.
4. They are heterotrophs (acquire nutrients by absorption).
B. Fungal life cycle
C. Ecological Roles of Fungi:
1. Decomposers – absorb nutrients from dead
organic matter, thereby decomposing it. Recycle
nutrients to the soil.
2. Parasites – absorb nutrients from living hosts.
ex. pathogens on crops
3. Mutualists with plants – absorb nutrients from host, but
aid host in mineral uptake from soil. ex. mycorrhizae
D. Lifestyles of Fungi
1. Molds: rapid growing, asexually reproducing fungi
2. Yeasts: single-celled fungi inhabiting moist habitats.
Raise bread & ferment alcohol
3. Lichens: symbiotic association of cyanobacteria or
green algae and fungi.
a. Fungus provides shape and attachment
b. Algae provides food, N to the fungus
c. Lichens are very sensitive to air pollution; used
as indicators of air quality.
4. Mycorrhizae: mutualistic association of plant roots
and fungi.
a. Fungus increases the absorptive surface area of
roots, increasing water and potassium uptake
b. Fungus receives food from the root exudates.
Pay heed to life’s lessons.