THELYPTERIDACEAE (Marsh Fern Family)

Plants perennial, homosporous, with rhizomes. Leaves variously lobed to compound, usually with stiff, needlelike hairs. Veins free (anastomosing elsewhere), branched. Sori globose to ellipsoid, produced along the veins. Indusia round to kidney-shaped or absent. Sporangia with the annulus an interrupted, vertical ring of cells. Gametophytes green, flat, obcordate to kidney-shaped, usually hairy or glandular. Three genera, about 900 species. Nearly worldwide, but most diverse in tropical regions.

Generic delimitations within the Thelypteridaceae remain controversial. Although various groups of related species are relatively well defined, various authors have recognized 1–30 genera, with varying numbers of subgenera. The present treatment follows that of Smith (1993) in the Flora of North America, which includes three genera for North America north of Mexico. Of these, two are present in Missouri. The third genus, Macrothelypteris (H. Itô) Ching, contains species native to the Old World tropics, one of which has become naturalized in the southeastern United States.