Kingdom Plantae: from algae to flowering plants

Every plant is many-celled, makes food by photosynthesis, and has cells boxed in by a rigid wall that is mostly cellulose, which supports and protects them. Plants sit at the base of most food chains and give off the oxygen that animals need.

The kingdom has five classes. Read them left to right as a journey out of the water. Switch on a feature to see which groups have it; tap a group to open it.

Read the key left to right and a story appears. The first plants let the water around them do two jobs, holding them up and ferrying their sex cells. Leaving the water meant replacing both, and the groups did it in instalments: plumbing first (xylem and phloem), seeds next, flowers and fruits last. No group is simply better; each trades off growth, transport, reproduction and survival in its own way.

The name says it: thallos is an undifferentiated body and phyton a plant. A thallophyte has no root, stem or leaf, just a thallus, a simple body that takes in water, nutrients and gases straight from the water around it. That suits life in water or very damp places. Spirogyra, a green thread with ribbon-like chloroplasts wound in a spiral, is a common example.

Bryophytes (bryon, moss) include mosses and liverworts such as Marchantia. After a few weeks of monsoon rain, check the shady side of an old wall or a wet boulder: the soft green carpet there is usually a bryophyte. Their body is more divided than a thallus: thread-like rhizoids anchor them, and they may have simple stem-like and leaf-like parts. They have no true roots, stems or leaves, and no tissue to carry water and food.

To make the next generation, a moss needs a film of water: its male cells have to swim across to the egg. Living on land, breeding through water: hence the nickname, the amphibians of the plant kingdom. Mosses are a snapshot of plants partway onto land, still leashed to moisture.

Ferns (pteron, feather, after their feathery fronds) have true roots, stems and leaves. How does water reach every frond? A good guess is a special transport tissue, and you can test the guess: cut a thin cross section of a fern stem, or use a school slide, and look under a microscope. You find vascular tissue, xylem carrying water and phloem carrying food, all through the plant.

Now compare it with the sunflower stem from Chapter 3.

For all their plumbing, pteridophytes still need water for reproduction, and they make no seeds.

Gymnosperms (gymnos, naked; spermos, seed), such as pines and cycads, cope well with cold, dry places. Thin needles or tiny scales instead of broad leaves mean little water escapes. They make seeds, which shield the young embryo and pack food for it, and fertilisation no longer needs water. No fruit wraps the seeds; they sit open on the scales of cones.

Angiosperms (angeion, vessel), the flowering plants, have the most complex bodies of all. Flowers bring in insects and birds that move pollen; fruits get the seeds carried off to fresh ground. With these, angiosperms have spread into almost every kind of habitat, and no other plant group comes close to their variety. The gulmohar is one.

Flowering plants are often split by their leaves. Sort these by their veins.

Parallel veins usually mean a monocot, a net of veins a dicot. Collect leaves near you and try the same sort for real.

Table 12.3 asks you to weigh each plant group: what helps it survive, and what holds it back. Sort the statements below; the group each belongs to is printed under it.

Then add a line of your own to each column of your table. For example: bryophytes stay small because they have no transport tissue; angiosperms can grow in deserts, wetlands and mountains.