Didymodon Hedw., Sp. Musc. Frond. 104. 1801.
Plants small, medium- or robust-sized, yellow-green, green, dark-green, red, or brown above, brown to reddish brown below, in loose tufts or cushions. Stems erect, sparsely and irregularly branched, sclerodermis present, central strand present or absent; rhizoids reddish brown, sparse. Axillary hairs 3–7 cells long, basal 1–3 cells quadrate and brown, upper cells hyaline. Leaves triangular-ovate, oblong-, ovate-, or linear-lanceolate, lanceolate, lingulate, ovate, elliptic, erect-appressed, erect-incurved, at times contorted or circinate-contorted when dry, variously grooved along the costa on upper ventral surface; apices rounded to obtusely acute, acute, acuminate or subulate; lamina unistratose, at times bistratose at the margins; margins entire, at times crenulate by projecting cells, recurved, revolute or plane; costa subpercurrent, percurrent or excurrent, ventral superficial cells quadrate or elongate, guide cells present, ventral stereid cells present or absent, dorsal stereid cells present, ventral surface layer of enlarged cells present or absent; upper cells quadrate, rounded, oblate triangular, or short-rectangular, firm-walled, pluripapillose, unipapillose or smooth, basal cells rounded, oblong, short- or long-rectangular, usually smooth, alar cells not differentiated. Asexual reproduction by propagula on rhizoids or in leaf axils. Dioicous. Perichaetia terminal. Setae elongate, smooth. Capsules cylindrical; stomata in neck; opercula long-conic to rostrate; annuli well-developed; peristome well-developed (teeth filamentous and twisted or short and erect), rudimentary or absent, basal membrane low or absent. Calyptrae cucullate.