Filices
One of the most important orders of acotyledons or cryptogams. Perennial (very rarely annual) herbs, sometimes shrubby or arborescent, with fibrous roots or creeping rootstocks. Leaves (fronds) tufted or alternate on the rootstock, simple, pinnatifid, or one to four-pinnate, usually circinate in vernation; petiole (stipes) sometimes jointed at the base and rachis, grooved on the upper surface. Fructification of microscopic spores, contained in usually minute capsules that are collected in masses (sori) on the under surface or edge of the frond, or rarely on separate fronds or parts of the frond, and are naked, or covered with an involucre formed of or upon the margin or back of the frond. Capsules membranous, sessile or stalked, often mixed with jointed club-shaped hairs (imperfect capsules). Spores usually obtusely tetrahedral. There are about seventy-five genera and about 2,500 species. The following genera contain the largest number of species: Acrostichum, Adiantum, Aspidium, Asplenium, Nephrodium, Polypodium, and Pteris.