Plants and red algae

Long ago, a tiny living thing swallowed a cyanobacterium and did not digest it. It kept it as a living solar panel to make food from sunlight. That one partnership gave rise to a surprising family: green plants and red algae, distant cousins sharing the same inherited sun-catcher. There is also a small third group of single-celled algae.

Land plants are the familiar green side: green shoots, often with stems and flat leaves and roots below ground. In different subgroups there are flowers, fruits, cones or spores. They sit inside a wider green group. The green algae grow as bright green sheets, hair-like threads, pond scum, or single cells too small to see. Red algae have no true leaves, stems, roots, flowers or seeds. They grow as thin sheets, delicate branching threads, or hard pink crusts and skeletons that feel like stone. Many are rose-red, wine-red, pink or purple, though some look olive-brown or green-blue.

You can find this family almost everywhere. Red algae live mostly in the sea, most diverse in warm, clear coastal waters from rock pools to deep slopes. Green algae live in seas, ponds, lakes and damp soil. Land plants rule the land, from forests and grasslands to deserts, mountains and cities. On land, they grow almost everywhere except the harshest ice and the driest deserts. No land plants live in the deep ocean. Members range from single cells too small to see to tall forest trees.