Fern

noun

Herbs with broad but highly dissected leaves and no flowers. A leafy plant of the phylum Filicinophyta (or, in traditional classifications, the class Filicinae - See pteridophyte) spread by spores, not seeds. Like mosses and liverworts, clubmosses and horsetails, ferns grow in two physically distinct forms that alternate during their life cycle. For the main part of this cycle, a fern consists of a short stem (rhizome) from which roots grow down into the soil, and leafy fronds grow upwards. This is called the sporophyte generation because it produces spores inside spore cases on the underside or margins of the fronds. These spore cases open and scatter the spores which, when they fall on moist soil, germinate to produce heart-shaped plants 2 to 3 cm (about an inch) across, called prothalli. These bear the sex organs, which in ferns are cavities containing microscopic egg cells and sperms. The sperms swim to fertilize the egg when the prothallus is wet, so ferns are able to reproduce sexually only in damp habitats. After fertilization the egg cell develops into a new sporophyte plant. Some ferns reproduce asexually by leaf buds or, in the case of bracken, by rhizomes. Many fossil ferns are known, some of which, unlike modern ferns, had seeds. About 9,000 species of living fern are known. The species Ophioglossum, known as adder's tongue, has the highest known chromosome number of any plant (over 1,000). This indicates an ancient lineage. Common temperate species include lady fern, Anthyr ium filix-femina, male fern, D. filix-mas, polypody, and bracken, Pteridium aquilinum. A non-flowering, vascular plant of the class Polypodiopsida.