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 PLANTS FOR 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 water by evaporation Maintaining an extensive moist surface for gas exchange Supporting a large plant body against gravity Carrying out reproduction when there is little water

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

Land Plants Evolved from Green Algae. 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 with an outer layer of jacket cells Cuticles 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)

Cooksonia, a Vascular Plant of the Silurian Period 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 the Four 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

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Some Highlights of Plant Evolution 140 mya 360 mya 420 mya 475 mya

Reduction in the Size of the Gametophyte

Bryophytes Liverwort Liverwort Hornwort Moss

Moss with Sporophytes Gametophytes

Liverwort, Marchantia Antheridia Archegonia

Hornwort – a Characteristic Bryophyte

Moss (Polytrichum) Life Cycle

The life cycle of Polytrichum, a moss

Pteridophytes Club Moss 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

Horsetail Horsetails and the other seedless vascular plants have highly branched vascular systems called megaphylls.

Fern sporophyll, a leaf specialized for spore production

Fern Sori (clusters of sporangia)

modified leaves with sporangia Most seedless vascular plants 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

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

Seeds Female Gingko

The Ginkgo Tree

Male Female

Phylum Cycadophyta: Sago Palm/Cycad

Sago Palm or Cycad, a gymnosperm

Sago Palm or Cycad Cones Figure 24.19

Phylum Gnetophyta: Welwitschia

Phylum Gnetophyta: Ephedra

Ephedra Figure 24.21

Phylum Coniferophyta: Douglas Fir

These are male cones on a pine tree.

Female Pine Cone Male Pine Cones

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

This picture is of “The Lone Cypress” taken on the 17 mile 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)

The Structure of a Flower

Generalized Flower Structure

Angiosperm Life Cycle

The Life Cycle of an Angiosperm