ADIANTACEAE

one of several families in the fern order Filicales. It consists of about 60 genera with 850 species and is distributed throughout the world, especially in tropical America. The family is characterized by spore-producing structures (sporangia) located in lines along the veins of the leaves or on or at the vein tips; these structures may be unprotected (lacking indusium), in grooves, or covered by the rolled leaf margin (false indusium). The best-known species of Adiantaceae are found in the subfamily Adiantoideae. The maidenhair fern (genus Adiantum) has about 200 species and shows glossy, usually smooth fronds and characteristic architecture. The Northern maidenhair (Adiantum pedatum; see ) is found in woods of North America and East Asia. Also found in Adiantoideae are the cliff brakes (Pellaea) and lip ferns (Cheilanthes), both of which tend to grow on rock cliffs or ledges. In this classification, a second subfamily, Vittarioideae (shoestring ferns), contains seven genera, the largest being Vittaria and Antrophyum, both found throughout the tropics.