fern

Any of about 10,000–12,000 species (division Pteridophyta) of nonflowering vascular plants that have true roots, stems, and complex leaves and reproduce by 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 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.

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