Ferns are the biggest and most diverse group of non-flowering plants, with about 11,000 species. Most species live in the tropics and many are epiphytes on trees. They typically have large feathery leaves or fronds which are tightly coiled when young, unwinding as they expand. Some ferns are large enough to be called tree ferns but they do not develop a trunk structure, the stalks of the fronds sprouting directly from a rhizomous rootstock. The reproduction of ferns is complex. Spores are produced on the undersides of the fronds. If these fall in a suitable damp place they develop into small heart-shaped structures called prothalli. After a further sexual stage, a new plant grows from a female prothallus.
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