ASPLENIACEAE

Chain fern (Blechnum spicant) Hart's tongue fern (Phyllitis) Maidenhair spleenwort (Asplenium) the most common and the largest of 11 families in the fern order Polypodiales (in other classification systems, one of five families of the order Aspidiales). Of worldwide distribution, the group contains some 60 to 80 genera and approximately 3,000 species. It is sometimes separated into three subfamiliesDryopteridoideae, Blechnoideae, and Aspleniodeae. The family includes such well-known plants as the woodferns and shield ferns (Dryopteris), holly ferns (Polystichum), halberd ferns (Tectaria), lady ferns (Athyrium), marsh ferns (Thelypteris), chain ferns (Blechnum and Woodwardia), hart's-tongue ferns (Phyllitis; see photograph), spleenworts and bird's nest ferns (Asplenium; see photograph), and walking ferns (Camptosorus). The family is characterized by scaly creeping stems, or rootstocks (rhizomes), spore-producing structures (sporangia) with stalks and a ring of thickened cells (annulus, or bow), the sporangia in clusters (sori) on the lower surfaces of the leaves and covered with shieldlike, kidney-shaped, oblong, or linear membranous protective structures (indusia). The spores are mostly bean-shaped (bilateral).