Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
Hymenophyllaceae
Genus Description - Mostly epiphytic, less commonly epipetric or even terrestrial; rhizomes long-creeping, thread-like, hairy, the hairs basifixed or centrally attached; fronds small; stipes slender to stout, glabrous to hairy; blades pinnatifid to several times pinnate; laminae generally one cell thick, often completely glabrous, some with hairs on leaf tissue, veins, and/or margins; sori marginal, in bilabiate involucral cups; sporangia borne on short to long receptacles; spores tetrahedral-globose, green; gametophytes of branched ribbons.
Lectotype (chosen by C. Presl, Hymenophyllaceae 31. 1843): Hymenophyllum tunbrigense (L.) Sm.
Sphaerocionium C. Presl, Hymenophyllaceae 33. 1843. Lectotype (chosen by Copel., Philipp. J. Sci. 64: 10. 1937): Sphaerocionium hirsutum (L.) C. Presl [= Hymenophyllum hirsutum (L.) Sw.]. Hymenophyllum subg. Mecodium C. Presl ex Copel., Philipp. J. Sci. 64: 93. 1937. Mecodium (C. Presl ex Copel.) Copel., Philipp. J. Sci. 67: 17. 1938. Lectotype (chosen by Copel., Phillip. J. Sci. 64: 10. 1937): Hymenophyllum polyanthos (Sw.) Sw. [= Trichomanes polyanthos Sw.]. For more complete synonymy, see Morton, 1968.
In a broad sense, the genus contains over 300 species, about one third of them neotropical, with a few species into wet temperate areas. Some authors, such as Copeland (1937), have split the genus into several genera. Hymenophyllum is distinct in its thin blades and bilabiate involucres with receptacles usually not exserted; x=11, 13, 18, 21, 22, 28, 36