Kingdom Plantae

Having already studied the general principles of classification, this chapter looks at how Kingdom Plantae itself is split into smaller groups. Botanists sort plants using three broad yardsticks: whether the plant produces seeds or not, whether it has specialised water- and food-conducting (vascular) tissue, and how far the plant body is differentiated into distinct root, stem and leaf regions.

Using the seed criterion first, Kingdom Plantae is divided into two sub-kingdoms:

• Phanerogamae (from phaneros, meaning visible) are the seed-bearing plants. Their reproductive organs mature into structures we can see with the naked eye — flowers, cones and eventually seeds — so their mode of reproduction is 'open' to observation.
• Cryptogamae (from kryptos, hidden, and gamos, marriage/union) are the spore-bearing plants. They reproduce sexually through gametes, but their sex organs are concealed within the plant body, and they never form true seeds or flowers.

Cryptogamae is further split by body organisation and the presence of vascular tissue into three groups — Thallophyta and Bryophyta (both non-vascular) and Pteridophyta (the only vascular Cryptogams). Phanerogamae is split into Gymnospermae (naked-seeded) and Angiospermae (seeds enclosed in a fruit), and Angiospermae is split again into Dicotyledonae and Monocotyledonae. The rest of this chapter examines each of these groups in turn, moving from the simplest algae to the most advanced flowering plants.