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