A group of some 12 000 mainly terrestrial vascular plants (see tracheophyte) traditionally classified in the phylum Pteridophyta. In this broad sense, ferns include clubmosses, whisk ferns, and horsetails as well as ‘true’ ferns. However, it is now recognized that clubmosses and their allies (see lycopodiophyta) are only distantly related to other ferns and that the latter constitute a distinct clade, the monilophytes, with closer affinity to the seed plants. The 9000 or so species of true ferns—the so-called leptosporangiate ferns—are perennial plants bearing large conspicuous leaves (fronds: see megaphyll) usually arising from either a rhizome or a short erect stem. Bracken is a common example. Only the tree ferns have stems that reach an appreciable height. As the young leaves expand into the adult form there is a characteristic uncurling from a structure called a ‘fiddlehead’, which resembles the scroll at the head of a violin. Reproduction is by means of spores borne on the underside of specialized leaves (sporophylls).