Monographs Details: Helicodontium
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)
Family:Myriniaceae
Scientific Name:Helicodontium
Description:Genus Description - Plants slender, in dull, green to brownish-green, ± wiry mats. Stems with an outer layer of 3-4 rows of smallish, thick-walled cells, toward the center becoming larger and thinner-walled; branches varying in length, often ascending. Stem and branch leaves scarcely differentiated, appressed when dry, erect- to wide-spreading when moist, ovate-lanceolate to ovate or oblong-ovate, acute to short-acuminate (rarely blunt), slightly decurrent; margins plane, serrulate above; costa usually strong, extending 3/4 the leaf length, rarely shorter; cells rounded-rhombic to long-hexagonal above, becoming longer toward the leaf base; alar cells quadrate. Autoicous. Perichaetial leaves short-acuminate. Setae erect, smooth or slightly roughened above, reddish; capsules ovoid to short-cylindric, slightly contracted below the mouth when dry; annulus none; operculum obliquely rostrate; exothecial cells short-rectangular, ± thick-walled, becoming smaller and thinner-walled in 1-3 rows at the mouth; peristome attached at the mouth; exostome teeth lanceolate, yellow to brownish-gray, cross-striolate at front, with projecting, non-omamented lamellae at back; endostome with a moderately high, smooth basal membrane, the segments about as long as the teeth, yellow to brown, narrow, keeled, perforate, and papillose, cilia lacking; columella cylindric, extending nearly to the mouth. Spores papillose. Calyptrae naked.

Discussion:Although the genus is often cited as Helicodontium (Mitt.) Jaeg. of 1878, it is clear that Schwaegrichen's 1830 description was meant to be generic. Following the generic description is the one for H. tenuirostre, the type species. (The only other species that Schwaegrichen described, H. fabronia, is now placed in Schwetschkeopsis.)