Concept preview

What you will be able to do

1. 01Name the four main groups of plants and place them in order of increasing adaptation to land.
2. 02Explain the key challenges of moving onto land and the adaptations that solved them (cuticle, stomata, vascular tissue, seeds, flowers).
3. 03Describe alternation of generations and how the balance of sporophyte and gametophyte shifted through plant evolution.
4. 04Use simple features to decide which group an unfamiliar plant belongs to.

For most of its history, life on Earth stayed in the sea, and the ancestors of today's plants were green algae floating in shallow, sunlit water. Water is a wonderfully forgiving place to live: it holds a cell up against gravity, it never lets the cell dry out, and it carries dissolved gases and minerals right to the surface of every part. Roughly 470 million years ago, some green algae made one of the boldest moves in the whole story of life and began to colonise the bare, rocky land. On land there is far more light and far more carbon dioxide, but the price is steep, because air dries living tissue out, gravity pulls it down, and there is no water to carry the sperm from one plant to the next. The entire evolution of plants is, in a sense, the long story of solving these four problems, and the four great groups of plants mark the milestones along that journey.