Evolution and
Diversity of Plants
Chapter 24
Evolution
Modern day plants evolved from freshwater
green algal species
● Evidence
o both contain chlorophyll a and b
o store excess energy as starch
o have cellulose cell walls
Stone warts are the closest DNA relative
Evolution had 4 major events
1-Nonvascular plants have multicellular
embryos that are protected and nourished
within structures that produce eggs
2- Seedless vascular plants- Vascular tissue
conducts water and organic nutrients within
its roots, stems, and leaves Approx- 430
million years ago
Evolution had 4 major events
3- Gymnosperms- Seeds produced in
cones. These highly resistant structures are
capable of waiting for a favorable
environment before germinating. Approx400 million years ago
4- Angiosperms- Seeds protected by fruits
and the presence of flowers with a need for
pollinators. Approx- 135 million years ago
Alternation of Generations
Alternation of Generations
2 multicellular individuals alternate, each
producing each other.
1. sporophyte (2n)- produces spores through
meiosis
2. gametophyte (n)- produces gametes
Alternation of Generations
Meiosis produces haploid spores in
sporophytes. Spores go through mitosis and
become gametophytes. Zygotes go through
mitosis to produce sporophytes
Alternation of Generations
Plants differ as to which generation is
dominant.
Archegonia→ female gametophyte
Antheridia→ contain flagellated sperm
Pollen Grains→mature sperm from seed
plants
Other adaptations
Cuticles
Stomatas
Nonvascular Plants
● lack a specialized means of transporting water and
●
●
●
●
●
nutrients
lack true roots, stems, and leaves.
Bryophytes is used to describe nonvascular plants.
Gametophytes are the dominant generation.
Sperm must swim in film of water to archegonia.
May reproduce asexually, allowing them to live in harsh
environments
Hornworts- Phylum Anthocerophyta
“Herb”
Live in moist, well-shaded trees
May have symbiotic relationship with
cyanobacteria
Can reproduce asexually through
fragmentation
Liverworts- Phylum Hepatophyta
Terrestrial, epiphytic, or aquatic
Majority have leafy bodies
Thallose grow on creek banks after a fire
Marchantia
Lower surface has hair like extensions
called rhizoids.
Rhizoids are for anchorage and limited
absorption.
Sexually and asexually reproduces.
Moss- Phylum Bryophyta
3 Distinct Classes:
Peat Moss
True Moss
Rock Moss
May live in almost any environment.
Moss reproduction
May reproduce
asexually through
fragmentation
Sexual reproduction is
depicted to the right
Vascular Plants- Phylum
Rhyniophyta
Early vascular plants were homosporous
Dominant sporophyte generation has several
characteristics that allowed for successful colonization of
land
● Xylem- water and dissolved minerals upward
● Phloem- sucrose and other organic materials
throughout the plant
● Lignin- strengthens plants
Now seed plants are heterosporous.
Seedless Vascular Plants
Dominant through the Devonian period to
the Carboniferous period
Club Moss- Phylum Lycophyta
Dominant generation is the sporophyte
Rhizome- horizontal underground stem
3 genera:
● Ground Pines-microphylls, homosporous
● Spike Mosses-macrophylls,
heterosporous
● Quillworts-macrophylls, heterosporous
Horsetails- Phylum
Sphenophyta
Inhabit wet, marshy
environments
Strobilus
Branches
Node
Leaves
Rhizome
Roots
Whisk Fern- Phylum
Psilotophyta
Live in southern climates as epiphytes or on
the ground
Have no leaves
Sporangia found on short side branches
Ferns- Phylum Pterophyta
Found in warm, moist, tropical
regions
Fronds are leaves of ferns divided
into leaflets
Can be used to remove
formaldehyde from the air, expel
tapeworms, and have medicinal
value
Seed Plants
-Devonian period
-Seeds contain sporophyte embryo and stored
food within a protective coat
● can remain dormant for hundreds of years
-Heterosporous
● pollen grains contain multicellular male
gametophyte
-No exterior water required for fertilization
-Female gametophyte develops in ovule
Gymnosperms (naked seed)
- All have ovules and exposed seeds
- Carboniferous period- became dominant
during Triassic period
Life cycle- see page 425 Figure
24.18
Conifers- Phylum Coniferophyta
- contains pines, spruces, firs
- majority bear cones
- phylum contains oldest tree and tallest
tree
- tough needle-like leaves conserve water
due to thick cuticle and recessed stomata
Phylum Coniferophyta
- sporophyte generation is
dominant- pollen is wind
blown and seed dispersal is
in dispersal stage
- monoecious- tree produces
both pollen and see
- used in construction, as
fungal and insect repellant
Cycad- Phylum Cycadophyta
- native to tropical and
subtropical areas
- resemble palms
- dioecious
- risk for extinction
because of slow growth
rate
Ginkgos- Phylum Ginkgophyta
- 1 surviving species
- dioecious
Gnetophyta- Phylum Gnetophyta
-
extremely diverse phylum
all have
-
-
similar xylem
no archegonia (evidence to
support them being closest
relative to angiosperms)
cones have similar
construction
Angiosperms
- ovules always enclosed within diploid tissues
- DNA sequencing is being used to determine ancestry
- 2 classes
- Monocotyledones- monocots- 1 seed leaf in seeds.
Corn, tulips, and pineapples are examples
- Eudicotyledones- dicots- 2 cotyledones in seeds.
Strawberries, cactus are examples.
Monocots
Dicots
One Cotyledon
Two Cotyledon
Flower parts in threes or multiples of three
Flower parts in fours or multiples of fours
Usually herbaceous
Woody or herbaceous
Usually parallel venation
Usually net venation
Scattered bundles in stem
Vascular bundles in ring
Fibrous root system
Taproot system
Flower parts
● Sepals- (calyx) protect the flower bud before it opens. May fall off
or remain attached. May be green or colored
● Petals- (corolla) attract a particular pollinator. Very diverse
● Stamens- consist of the anther, saclike, and filament (slender stalk)
● Carpel- vaselike- made of stigma, enlarged sticky knob; style,
slender stalk; ovary, enlarged base that encloses one or more
ovule. Ovule becomes seed and ovary becomes fruit
● Flowers may or may not have all the above parts (incomplete)
Life cycle- see page 430
Figure 24.26