Weissia controversa Hedw., Sp. Musc. Frond. 67. 1801.
Protologue: Germany. Lipsiae ad rivulum post collem Bienitz.
Hymenostomum mexicanum Card., Rev. Bryol. 36: 70. 1909. Protologue: Mexico. Etat de Jalisco: Etzatlan, 1908 [Pringle] (n 15270).
Plants small, dark-green to yellow-green above, brown below, in dense mats or tufts, 2.5–5 mm high. Stems red, sparsely and irregularly branched, hyalodermis weakly developed, central strand well-developed; rhizoids sparse, red, smooth to roughened. Leaves 1.3–2.3 mm long, linear-lanceolate to lanceolate, ovate to oblong, weakly clasping to erect at base, crisped and spirally contorted above when dry, erect-flexuose to erect-spreading when wet; apices acuminate, mucronate; lamina unistratose, not fragile; margins entire, strongly involute above the base to the apex; costa stoutly excurrent, broad at base (40–80 μm), ventral surface cells quadrate, guide cells and two stereid bands well-developed, ventral surface layer enlarged, papillose, green; upper cells rounded to quadrate, 6–11 μm long, thick-walled, bulging at the surface, with 4–6 bifid papillae, basal cells narrowly rectangular, thick- or thin-walled, yellow or hyaline, smooth, 20–50 x 6–10 μm, outer basal cells hyaline, thin-walled, not or somewhat running up the margins in a v-shaped pattern. Autoicous. Perichaetial leaves somewhat larger and longer than vegetative leaves, otherwise not strongly differentiated. Sporophytes not known from Central America. Setae smooth, 4–8 mm long, yellow. Capsules ovoid to oblong, erect, 0.8–1.2 mm long, somewhat furrowed when dry; stomata in neck; opercula rostrate, 0.7–1.0 mm long; annuli of several rows of cells persistent cells; peristome teeth 16, short, narrowly triangular, erect, red, papillose, basal membrane absent, rudimentary or absent. Spores 18–22 μm, papillose. Calyptrae yellow, cucullate, smooth, 1.2 mm long.