Any of about 10,000–12,000 species (division Filicophyta) of nonflowering spores .
Though ferns were once classified with the primitive horsetails and club mosses , botanists have since made a clear distinction between the scalelike, one-veined leaves of those plants and the more complexly veined fronds of the ferns, which are more closely related to the leaves of seed plants . Ferns come in a wide variety of sizes and shapes. Many are small, fragile plants; others are treelike (see {{link=tree fern">tree fern ). The life cycle is characterized by an alternation of generations between the mature, fronded form (the sporophyte ) familiar in greenhouses and gardens and the form that strongly resembles a moss or liverwort (the gametophyte ). Ferns are popular houseplants.