Plant Evolution and Classification
Overview of Plants
I. Adapting to land
a. organisms lived in oceans until about 430 million
years ago when the ozone formed
b. Preventing water loss
i. Land advantages
1. more sunlight
2. increased carbon dioxide
3. supply of inorganic nutrients
ii. Land challenges
1. drying out through evaporation
iii. Adaptations
1. cuticle - waxy protective covering on
plant surfaces that prevents water loss
a. keeps water in and CO2 out
b. stomata - small openings in surface
which allow exchanges of CO2 and O2
c. Reproducing by Spores and Seeds
i. Spore - contains a haploid reproductive
cell surrounded by a hard outer wall
ii. Seed - embryo surrounded by a
protective coat
1. endosperm - in seeds, tissue that
provides nourishment for the
developing plant
d. Transporting materials throughout the plant
i. Vascular tissue - tissue that transports
water and dissolved substances from one
part of the plant to another
1. Xylem - H20 and Inorganic nutrients
roots to stems and leaves
2. Phloem - organic compounds
(carbohydrates) and inorganic
nutrients in any direction
3. helps support the plant
4. Woody Tissue - several layers of xylem
a. Herbaceous - soft, green stems
II. Classifying Plants
a. Nonvascular plants - no true vascular tissue nor
true roots, stems or leaves
b. Vascular Plants - has vascular tissue and true
roots, stems and leaves
i. Seedless plants - ferns
ii. Seed Plants - plants that produce
seeds for reproduction
1. gymnosperms - pine trees, seeds
not enclosed in fruits
2. angiosperms - flowering plants,
seeds within a protective fruit
c. Alternating Life Cycles
i. 2 phases of plant life cycles
1. Gametophyte - haploid plant that
produces eggs and sperm
a. mitosis
2. diploid sporophyte plant that produces
spores
a. Meiosis
3. Cycling is called alternation of
generations
ii. Nonvascular plants - gametophyte is
the dominate phase
iii. vascular plants - sporophyte is the
dominant phase
Nonvascular Plants
I. Bryophytes
a. three phyla of nonvascular plants
i. 16,600 species
ii. lack vascular tissue, roots, stems and
leaves
iii. generally on land near streams and rivers
B. Classifying Bryophytes
i. Most primitive type of plant
1. seedless and produce spores
2. Need water to reproduce sexually
ii. Small (1-2 cm)
C. Phylum Bryophyta
i. almost every land environment is
home to atleast one species of
moss
1. rhizoids - rootlike structures
that do not have vascular tissue
2. Pioneer plants - first species
to inhabit a barren
area
3. accumulate inorganic
and organic matter
which creates a layer of soil
ii. Sphagnum - Peat moss
1. Partially decomposed plant
matter
2. Mined and dried for use as
fuel
3. produces an acid that slows
down decomposition in
swamplike bogs
4. enhances water retaining
ability of potting soils
5. used to pack bulbs
and flowers for shipping
d. Phyla Hepatophyta
i. liverworts - moist, shady areas
1. thin transparent leaflike
structures around a stemlike axis
2. thalloid - flat body with
distinguishable upper and lower
surfaces
3. close to ground to absorb
water
e. Phylum Anthocerophyta
i. includes hornworts - moist, shady
areas
1. cells have single large
chloroplast rather than many
small ones (algae)
liverworts
Hornworts
Vascular Plants
I. Vascular Plants
a. Have conducting tissues - xylem and phloem
b. grow larger and live in more environments than
nonvascular plants
II. Seedless Vascular Plants
a. dominated the Earth until about 200 million years ago
b. 4 Phyla - First 3 - Fern allies, last - Ferns
c. Spores are the mobile sexual reproductive part of all
seedless plant
d. Phylum Psilotophyta
i. represented by whisk ferns
1. not actually ferns
2. no roots or leaves and produce spores
on the ends of short branches (early land
plants)
3. epiphytes - grown on other plants but
not parasites
e. Phylum Lycophyta
i. contains club mosses
1. Also called ground pines (mini pine
trees)
2. Strobilus - cone structure
3. Sporangia-bearing modified leaves
ii. Spike Moss (Selaginella lepidophylla)
1. turns brown and curls up during a
drought but turns green again
when moistened
f. Phylum Sphenophyta
i. includes horsetails (Equisetum)
1. jointed photosynthetic stems that contain
silica and silklike leaves at each joint
2. pioneers used them to scrub pots and
pans (scouring rushes)
g. Phylum Pterophyta
i. Ferns
ii. originated over 350 million years ago
iii. some are floating plants
iv. grow above the Arctic Circles and in desert regions
v. Rhizome - underground
stems, often used as a
growing medium for orchids
vi. Fiddleheads - tightly coiled new leaves
1. uncoil and develop into mature fronds
III. Vascular Seed Plants
a. multicellular seed
i. allows greater chance for reproduction
ii. inside the seed in an embryo and a
nutrient supply
iii. When conditions favor growth the seed
sprouts (germinates) into a seedling
b. 2 groups - gymnosperms and angiosperms
c. Gymnosperms
i. 4 phyla
ii. produce naked seeds - not enclosed and
protected in fruits
iii. Mostly evergreen and bear their seeds in cones
1. cone - reproductive structure composed
of hard scales
d. Angiosperm
i. seeds that are enclosed and protected in fruits
ii. commonly referred to as flowering plants
e. Phylum Cycadophyta
i. Cycades
1. Flourished during the age of the
dinosaurs
2. only 100 species survive today
3. native to the tropics and grow slowly
4. endangered because of habitat loss,
over-collection, and their slow growth
5. fernlike, leathery leaves at the top of a
short, thick trunk
6. male or female
7. bear large cones
f. Phylum Ginkgophyta (gymnosperms)
i. Ginkgoes - flourished during the time of the
dinosaurs
ii. Only existing today is Ginkgo biloba (china)
i. called living fossil
iii. Fan-shaped leaves that fall from the tree at the
end of each growing season
1. Deciduous - lose their leaves at the end
of the growing season
iv. Most gymnosperms are evergreens and retain
their leave year-round
v. Tolerant of air pollution
vi. Plum-shaped fleshy seeds
g. Phylum Coniferophyta (gymnosperms)
i. conifers - pine, cedar, redwood, fir, spruce, juniper,
cypress, and bald cypress
ii. Important sources of wood, paper, turpentine,
resin, ornamental plants, and Christmas trees
iii. woody plants and most have needles or scalelike
leaves
iv. bears both male and female cones
1. small male cones typically grow in
clusters and release clouds of dustlike
pollen, then fall from the branches
2. Pollen then blows into larger, woody
female cones, where the egg cells are
attached to the scales of the cone.
3. After pollination the female cone closes
up tightly, which protects the developing
seed until it matures after 1 or 2 years and
released when the female cone opens
v. Redwoods and giant sequoia trees are the tallest in the
world and the most massive living organism
h. Phylum Gnetophyta
i. odd group of cone bearing gymnosperms
ii. vascular systems that more closely resemble
those of angiosperms
iii. Includes the Ephedra
1. produces the drug ephedrine, a
decongestant
i. Phylum Anthophyta (angiosperms)
i. Largest phylum of plants
ii. over 240,000 species of flowering plants
iii. seed plants characterized by the presence of a
flower and fruit
1. fruit - ripened ovary that surrounds the
seeds of angiosperms
2. ovary - female part of the flower that
encloses the egg
iv. Herbaceous plants with showy flowers
1. violets and impatiens
v. Shrubs
1. rose bushes
vi. vines
1. Grape and ivy plants
vii. Flowering plants with woody stems
1. Oak, aspen and birch trees
viii. Grasses
IV. Evolution of Angiosperms
a. First appeared in fossil record 135 million years
ago
b. 90 million years ago angiosperms began to
outnumber gymnosperms
c. Advantages of angiosperms
i. seeds germinate and produce mature
plants all in one growing season
ii. Fruits protect seeds and aid in their
dispersal
iii. more efficient vascular system and are
more likely to be associated with
mycorrhizae
1. symbiotic relationships that form
between fungi and plants. The fungi
improve water and nutrient
absorption capabilities
iv. Animal pollination
v. More diverse (niches)
V. Monocots and Dicots
a. Flowering plants under phylum Anthophyta are
divided into 2 classes - Monocotyledones (monocotos) and
Dicotyledones (dicots)
i. Primary factor that distinguishes the
groups is the number of cotyledons in a
plant embryo
1. seed leaves
ii. Monocots
1. usually have 1 cotyledon in their embryo
iii. Dicots
1. typically have 2 cotyledons
2. Gymnosperms usually have 2 or more
cotyledons