Plants

The word ‘plants' can be used to refer to a wide range of living things, from blue-green bacteria through algae to multicellular eukaryotes which are grown and eaten by humans.

Plants are the only way in which sunlight energy can be turned into living material, so are fundamental to all other living things on Earth. Plants differ from animals in their source of energy and in their lack of mobility. Since sunlight will reach a plant if it stands still, there is usually no evolutionary benefit in a plant moving around. The exceptions are in blue-green bacteria and algae, which are often motile, and in the sex cells of plants or their embryos, which are not motile in themselves but are designed to be carried by wind, water or animals in order to disperse the plant.

Plants first appeared on Earth in the form of blue-green bacteria about 3.5 billion years ago. The algae appeared around 1.5 billion years ago, and colonies of them around 1 billion years ago. Land plants appeared around 500 mya and had evolved into tree ferns about 350 million.

Seeds appeared about 300 mya and fruits about 200 million.

Grasses, now the main diet of most animals including people, appeared about 50 mya.

Simplified family tree of green plants