Evolution of Land Plants

approx 1.2 billion years ago

approx 1.2 billion years ago

cyanobacteria likely existed on land

• fueled the oxygen revolution

approx 500 million years ago

small plants, fungi and animals emerged on land

approx 440 million years ago

diversification of early vascular plants

approx 300 million years ago

extensive forests of vascular plants form

• first seed plants appear

• origin of reptiles

• amphibians dominant

approx 200 million years ago

cone bearing plants (gymnosperms) dominate landscape

• dinosaurs evolve and radiate

• origin of mammals

approx 150 million years ago

gymnosperms continue as dominant plants

• dinosaurs are abundant and diverse

approx 100 million years ago

flowering plants (angiosperms) appear and diversify

• many groups of organisms, including most dinosaurs, go extinct

First plants

• lives underwater

• evolved from ancestors of green algae

• non-vascular and needed to grow directly on or near water

  • no roots or vascular tissue in their shoots

present day non-vascular plants

• mosses

• liverworts

• hornworts

Charophytes

green algae

• closest living relatives of land plants

• land plants evolved from these

Benefits of moving onto land

• unfiltered sunlight

• more carbon dioxide

• soil rich in nutrients

• few herbivores and pathogens

challenges of moving onto land

• scarcity of water

• lack of structural support against gravity

Adaptations to life on land

• structures to avoid drying out

  • waxy coat on leaves (cuticle)

  • stomata

• specialized tissues to transport water and nutrients throughout the plant (vascular tissue)

• sporopollenin

• tall stems and broad leaves to compete for sunlight

• roots to anchor the plant in the ground

Stomata

allow for the exchange of gasses but can close to prevent evaporative water loss

Sporopollenin

durable polymer that covers exposed zygotes of charophytes and is a major component of walls of spores/pollen

• a lot of plants in the water have free floating sperm that can swim around to find the female parts of another plant

  • this can’t happen on land

  • needed a new method to protect these gametes

how Vascular plants paved the way

• grew in rocky areas and turned rocks into soil

• took in CO2 and created a cooler habitat for other organisms to grow

• produced O2 to increase the atmospheric oxygen

Close to 500 million years ago

green algae existed

• ancestor to all land plants

Bryophytes

all plants that live on land that lack vascular tissue and large root systems

• small plants

• live close to the water

Evolution to have seeds

• embryo encased in a hard coating that is protective and can allow it to grow

• protect against dehydration

Seedless Vascular Plants

2 clades

• lycophytes

  • club mosses and their relatives

• monilophytes

  • ferns and their relatives