CHARACTERISTICS OF PLANTS:Eukaryotic Cells

Autotrophic and Multicellular

Cell Walls Contain Cellulose

Alternation of Generation

Embryonic Development

• More than 280,000 species of plants inhabit Earth today.

Land plants (including the sea grasses) evolved from a certain green algae, called charophytes

Spirogyra, a

model chlorophyte

CHALLENGES FACED BY PLANTSFOR LIFE ON LAND•Obtaining enough water

•Transporting water and dissolved substances to other parts of the plant body and transporting the products of photosynthesis to other parts of the plant that don't conduct photosynthesis

•Preventing excessive loss of waterby evaporation

•Maintaining an extensive moist surface for gas exchange

•Supporting a large plant body againstgravity

•Carrying out reproduction when thereis little water

•Lastly, withstanding the extremefluctuations in temperature, humidity, wind, and light which are moderated in water due to its high heat capacity

Land Plants Evolved from GreenAlgae.

Common Characteristics:•Rose-shaped complexes for cellu-lose synthesis•Peroxisome enzymes•Structure of flagellated sperm•Formation of a phragmoplast

Charophyceans: Chara (top), Coleochaete orbicularis (bottom)

Several Features of Land Plants Differ From Those of Green Algae

Multicellular sex organs withan outer layer of jacket cellsCuticles on leaves

Derived Traits of Land Plants

(These traits are absent in the charophyceans – next four slides)

Apical Meristems of Plant Shoots and Roots

Alternation of Generations: a Generalized Scheme

Multicelllular Gametangia: Archegonium of Marchantia (left), Antheridium of a hornwort (right)

Multicellular Dependent Embryos: Marchantia (left), Shepherd's purse (right)

Walled Spores Produced In Sporangia

Cooksonia, a Vascular Plant of the Silurian Period

Leaves of Vascular Plants

• There are four main groups of land plants:

• Bryophytes • Pteridophytes • Gymnosperms • Angiosperms – 90% of all

plants

Representatives of theFour Major Groups of Plants

• There are four great episodes in the evolution of land plants:

–the origin of bryophytes from algal ancestors

–the origin and diversification of vascular plants

–the origin of seeds

–the evolution of flowers

p. 578

Some Highlights of Plant Evolution

475 mya

420 mya

360 mya

140 mya

Reduction in the Size of the Gametophyte

Hornwort

Liverwort Liverwort

Moss

Bryophytes

Moss with Sporophytes

Gametophytes

Liverwort, Marchantia Antheridia Archegonia

Hornwort – a Characteristic Bryophyte

Moss (Polytrichum) Life Cycle

The life cycle of Polytrichum, a moss

Pteridophytes

ClubMoss

Whisk Fern

Horsetail Fern

Whisk Fern, Psilotum

Club Moss

Club Moss in Olympic National Forest – WA State

Club Moss in Olympic National Forest

Club mosses (Lycopodium) have microphylls, with single veins

HorsetailHorsetails and the other seedless vascular plantshave highly branched vascularsystems calledmegaphylls.

Fern sporophyll, a leaf specialized for spore production

Fern Sori (clusters of sporangia)

• Sporophylls

–modified leaves with sporangia

• Most seedless vascular plants

–Are homosporous, producing one type of spore that develops into a bisexual gametophyte

sporangium > single > bisexual > eggs and sperm type of gametophyte spore

• All seed plants and some seedless vascular plants

–Are heterosporous, having two types of spores that give rise to male and female gametophytes

megaspore > female gametophyte > eggs

microspore > male gametophyte > sperm

Fern Life Cycle

The Life Cycle of a Fern

• The first seed plants evolved about 360 million years ago, near the end of the Devonian Period.

• A seed consists of a plant embryo packaged along with a food supply within a protective coat.

The Reduced Gametophyte of Seed Plants are Protected in Ovules and Pollen Grains

From Ovule to Seed

Phylum Ginkgophyta

The Gingko (biloba) treeis a “living fossil”and has been on the earth virtuallyunchanged for at least 150 million years. It produces “naked” seeds, as do all other gymnospernms.

Female Gingko

Seeds

The Ginkgo Tree

Male Female

Sago Palm or Cycad, a gymnosperm

Sago Palm or Cycad Cones

Figure 24.19

Phylum Gnetophyta: Welwitschia

Phylum Gnetophyta:

Ephedra

Ephedra

Figure 24.21

PhylumConiferophyta:

DouglasFir

These are male coneson a pine tree.

Male Pine Cones

Female Pine Cone

This picture was taken in Sequoia National Park in Central California.One sequoia tree, nicknamed the “GeneralSherman Tree” is the heaviest/largest tree in the world. It is over 2300 years old and weighsover 1300 tons.

This picture is of “The Lone Cypress”taken on the 17mile drive on the Monterey Peninsula.It is one of the most commonly photographed trees in the world.

This picture is of the Bristlecone Pine Tree which is the oldest tree in the world – over 4700 years old.

“Methusaleh” as the oldest tree is called is located in the White Mountains of California.

Pine Life Cycle

The Life Cycle of a Pine

• The great majority (90%) of modern-day plant species are flowering plants, or angiosperms.–Flowers evolved in the early

Cretaceous period, about 140 million years ago.

–A flower is a complex reproductive structure that bears seeds within protective chambers called ovaries.

Representatives of Major Angiosperm

Clades

Figure 30.18 Flower-pollinator relationships: Scottish broom flower and honeybee (left), hummingbird (top right), baobab tree and bat (bottom right)

Generalized Flower Structure

Angiosperm Life Cycle

The Life Cycle of an Angiosperm