A family of ferns in which the sporangia are borne naked and singly on the margins of the leaves, sometimes protected by the incurved leaf margin. The sporangia are relatively massive, somewhat intermediate in character between those of eusporangiate and leptosporangiate ferns, with very short, thick stalks, and a terminal ring of thickened cells; they may contain more than 200 spores. All sporangia mature at the same time (a simple type of development). The gametophytes are either green and filamentous, like moss protonemata, or (in Actinostachys) may be fleshy, subterranean, cylindrical structures with mycorrhizal fungi. There are 4 genera and 150 species, mostly tropical, but the family extends into temperate parts of America.
Subjects: Plant Sciences and Forestry.