Plant Diversity

Where did plants evolve

• Evolved from green algae

• Charophyceans

• Closest living relatives of land plants

Plants moving to land

• Charophyceans (durable polymer - sporopollenin, prevents plants from drying out)

Derived traits of plants

• Alternation of generations

• Multicellular dependent embryos

• Walled spores produced in sporangia

• Multicellular gamete-producing tissue

• Apical meristems 

Origin and diversification of plants 

• 475 million years ago 

Mosses/bryophytes

• Dominated by gametophytes state

• Nonwoodu

• Liverworts

• Hornworts

• Mosses

Ecological and Economic importance of Mosses

• Peat moss

• Decayed organic material known as peat

• Traps lots of carbon

Vascular plants

• Tissue allows them to grow tall

• Diversify during the Carboniferous period 

• Dominant saprophytes 

Xylem

• Conducts most of the water and minerals

• Dead cells called tracheids

Phloem

• Consits of living cells and distributes sugars, amino acids, other organic products from leaves 

Evolution of roots

• Anchor vascular plants 

• Enable vascular plants to absorb water 

• Subterranean stems

Solution of leaves

• Leaves are organs that increase surface area of vascular plants 

Microphylls

• Leaves with a single vein

Megaphylls

• Leaves with highly branched vascular system 

Sporophylls

• Homosporous (one type of spore, bisexual gametophyte)

• Heterosporous (two types of spore that give rise to male and female gametophytes)

Significance of Seedless Vascular Plants

• Global cooling, withdrawing carbon from the atmosphere

• Carboniferous forests became coal

Seed plants

• Heterospor

• Reduced gamtophytes

• Ovules

• Pollen

Reduced Gametophytes

• Develop within the walls of spores, retained within tissues of the parent sporophyte 

Ovules

• Megasporangium

• Megaspore

• One or more protective layers (integuments)

Pollen

• Microspores develop into pollen grains

Pollination

• Transfer of pollen to the part of the seed with ovules 

Evolutionary advantage of seeds

• Develops from whole ovule

• Sporphyte embryo 

Gymnosperms

• Naked seeds

• Cycads

• Ginkgo

• Gnetum, Ephedra, Welwitschia

• Coniferophyta

Life Cycle of Pine

• Dominance of sporophyte generation

• Development of seeds from fertilized ovules

• Transfer sperm to ovules by pollen

Megasporocyte

• Female

• Ovule

Microsporocyte 

• Male

• Anthers

• Cones in gymnosperms

Angiosperm

• Flowers and fruits

• Most diverse plants 

Adaptations of Flowers

• Sepals (protect the plant)

• Stamens (produce pollen)

• Carpels (produce ovules)

• Petals (bright to attract pollinators)