PTERIDACEAE (Maidenhair Fern Family)

Plants perennial (rarely annual elsewhere), homosporous, with rhizomes. Leaves variously compound. Sporangia aggregated into sori on the undersurface of the leaves, submarginal or sometimes extending along the veins to nearly cover the leaf undersurface, exposed or partially covered by the recurved margin of the pinnules (known as a false indusium), the sporangial annulus an interrupted, vertical ring of cells. Spores 32 or 64 per sporangium, mostly brown to tan (black, gray, or yellow elsewhere), trilete. Gametophytes green, flat, obcordate to kidney-shaped. About 40 genera, about 1,000 species, worldwide.

The Pteridaceae are a large, widely distributed family that is well represented in seasonally dry regions of the world. Many of the species have highly modified leaves with small, sometimes leathery leaflets and dense hairs, scales, farina, or other glandular exudates. In some species the leaves curl up during drought, but rehydrate following rain. These characteristics are presumably adaptations to life in dry environments. Hybridization, polyploidy, and apogamy also are common in the family. The family name Pteridaceae has priority over Adiantaceae, a name used in some older floristic manuals.