Plant Diversity

What Is A Plant?• Multicellular eukaryotes

• Cell walls with cellulose

• Photosynthesis using green pigments – chlorophyll a and b

• Autotrophs

• Some are parasites or saprobes

What Plants Need To Survive• Sunlight

• Water and minerals

• Gas exchange

• Movement of water and nutrients

Early Plants• For most of Earth’s history plants did not

exist

• Origins in the water

• Green algae: the first plants evolved from an organism much like the multicellular green algae living today

• Depended on water to complete their life cycles

The First Plants• Life on land favored the evolution of

plants: – More resistant to the drying rays of the

sun

– More capable at conserving water

– More capable of reproducing on dry land

The First Plants• Like today’s

mosses

• Gave rise to the plants of today!

– Non-vascular Plants

– Seedless Vascular Plants

– Gymnosperms

– Angiosperms

Four groups based on:

Water-conducting tissues

Seeds

Flowers

Today scientists can classify plants more precisely by comparing DNA sequences of various species

The Plant Life Cycle: Alternation of Generations

• Haploid gametophyte (N): gamete-producing phase of an organism

• Diploid sporophyte (2N): spore-producing phase of an organism

SEEDLESS PLANTS

Green Algae• First plants

• Mostly aquatic

• Fresh and salt water, some moist areas on land

• Absorb water and nutrients from surroundings

• Life Cycle: switch between haploid and diploid

• No specialized cells

Bryophytes• Mosses, liverworts, hornworts

• Depend on water

• Sperm swim through water to reach eggs of other plants

• No vascular tissue

• Can draw up water by osmosis only a few cm above the ground

Mosses• The most common bryophytes

• Well adapted to wet habitats and nutrient-poor soils

• Gametophyte dominant

• Reproduce produce thin stalks with sporophyte

• Rhizoids: long, thin cells that anchor them in the ground and absorb water and minerals from the surrounding soil

• No true roots

Life Cycle of A Moss• Archegonia: produces eggs

• Antheridia: produces sperm

• Sperm of the bryophyte must swim to an egg for fertilization to occur

• A diploid zygote results from fertilization

• Sporophyte: the zygote

• Grows out of the gametophyte and depends on it for water and nutrients

• When ready, haploid spores are released to start the cycle again

VASCULAR PLANTS

Vascular Plants: Tracheophytes• Vascular tissue: a type of tissue that is specialized

to conduct water and nutrients through the body of the plant

• Tracheid: hollow plant cell in xylem tissue with thick cell walls that resist pressure

• One of the great evolutionary innovations of the plant kingdom!

Vascular Plants• Xylem and Phloem:

– move fluids throughout the plant body

– even against the force of gravity

• Allow vascular plants to:

– grow upright

– reach great heights

Structure of Vascular Tissue• Xylem: vascular tissue

that carries water upward from the roots to every part of the plant

• Phloem: vascular tissue responsible for the transport of nutrients & carbohydrates produced by photosynthesis

Vascular Plants• Roots: absorb water and minerals

• Leaves: photosynthetic organisms that contain one or more bundles of vascular tissue

• Stems: supporting structures that connect roots and leaves, carrying water and nutrients between them

SEEDLESS VASCULAR PLANTS

Seedless Vascular Plants• Club mosses, horsetails, and ferns

• Ferns have survived Earth’s long history in numbers greater than any other group of spore-bearing vascular plants

• More than 11,000 species live today

• Strong roots

• Rhizomes: creeping or underground stems

• Fronds: large leaves

• Can thrive in areas with little light

• Most abundant in wet or seasonably wet habitats

Life Cycle of Ferns• Sporophyte = Dominant

• Produce haploid spores on the underside of their fronds in sporangia

• Spores are released

• Spores germinate into haploid gametophytes

• Diploid zygote is produced from fertilization

• Sporophyte grows and the gametophyte withers away

SEED PLANTS

Seed Plants• Seeds include:

– Acorns, pine nuts, dandelion seeds, kernels of corn, etc.

• Seed plants are divided into two groups:– Gymnosperms

– Angiosperms

Seed Plants• Reproduction free from water

• Can live just about anywhere

• Adaptations to reproduce without water:

– Flowers or cones

– Transfer of sperm by pollination

– Protection of embryos in seeds

Cones and Flowers• Gametophyte of

seed plants grow and mature within sporophyte structures called cones (gymnosperms) and flowers (angiosperms)

Pollen• Pollen Grain: male

gametophyte is contained in a tiny structure

• The wind, insects, birds and small mammals may carries pollen grains

• Pollination: the transfer of the pollen grain to the female gametophyte

Evolution of Seed Plants• The seed was very

important evolutionarily

• Seed: embryo of a plant encased in a protective covering and surrounded by a food supply

• Mosses and ferns underwent major adaptive radiation 300-400 mya

• Land environments were much wetter than they are today

• As the land became drier, it became harder for seedless plants to survive

• Fossils of seed-bearing plants exist from almost 360 mya

• The original seed plants resembled ferns

GYMNOSPERMS

Gymnosperms…Cone Bearers• The most ancient surviving seed

plants

• Include cycads, ginkgoes, and conifers

• “Naked Seed”: these plants all reproduce with seeds that are exposed

Conifers• The most common gymnosperms

with more than 500 known species

• Pines, spruces, firs, cedars, sequoias, redwoods, yews

• Some, like the bristlecone pine tree, can live for more than 4000 years

• Others, such as the giant redwood, can grow to more than 100 meters in height

Ecology of Conifers• Thrive in a wide variety of habitats: on mountains,

in sandy soil, and in cool, moist areas

• Leaves have adaptations to dry conditions

• The leaves are long and thin, like pine needles

• This shape reduces the surface area from which water can be lost

• Waxy layer also prevents water loss

• Most are evergreens: they retain their leaves through the year

Cones• Pollen Cones (male cones):

produce pollen

• Seed Cones (female cones): produce female gametophytes in two ovules

• The complete life cycle takes 2 years to complete

• The direct transfer of pollen to the female cone allows fertilization to take place without the need for gametes to swim through standing water

ANGIOSPERMS

Angiosperms…Flowering Plants• Flowering plants first

arrived about 135 mya

• Originated on land and became the dominant plant life on Earth

• The majority of living plant species reproduce with flowers

Flowers: An Evolutionary Advantage• Attract animals which transport

pollen from flower to flower

• More efficient than wind pollination of most gymnosperms

• Flowers contain ovaries, which surround and protect the seeds

Angiosperms…”Enclosed Seeds”

• After pollination, the ovary develops into a fruit, which protects the seed and aids in its dispersal

• Fruit: thick wall of tissue surrounding the seed

• Adds to the success of angiosperms

Monocots and DicotsMonocots• Angiosperm whose seeds

have one cotyledon

• Parallel veins

• Floral parts often in multiples of 3

• Stem vascular bundles are scattered

• Fibrous root

Dicots• Angiosperm whose seeds

have two cotyledons

• Branched veins

• Floral parts often in multiples of 4-5

• Stem vascular bundles are arranged in a ring

• Taproot

Comparing Monocots and Dicots

Woody Plants• Woody plants are made

primarily of cells with thick cell walls that support the plant body

• Trees– All types!

• Shrubs– Blueberries,

rhododendrons, roses

• Vines – Grapes and ivy

Herbaceous Plants• Smooth and non-

woody plants that do not produce wood as they grow

• Dandelions, zinnias, petunias, sunflowers

Growing Season• Annuals: Flowering plants that complete a life

cycle within one growing season

– Garden plants, marigolds, petunias, pansies, zinnias, wheat and cucumbers too!

• Biennials: Flowering plants that complete a life cycle in two years

– Primrose, parsley, celery, foxglove

• Perennials: Flowering plants that live for more than two years

– Peonies, asparagus, grasses: herbaceous perennials

– Palm trees, sagebrush, maple trees, honeysuckle: woody perennials