Didymodon

Description

Plants growing in dense or loose turfs, green brown, reddish brown, red, glaucous, olive-green or blackish. Stems erect or more rarely decumbent, simple or branched, ocasionally with deciduous flagelliform innovations, without hyalodermis or seldom differentiated, sclerodermis usually developed, with central strand, very rarely undifferentiated; axillary hairs filiform, 2–8 cells long, with 1–2(3) brown basal cells and hyaline upper cells. Rhizoidal tubers underground or on rhizoids in the lower part of the stem, multicellular, rounded to elongated, straight or variously curved, brown, smooth. Leaves monomorphic, very rarely dimorphic, appressed, incurved, twisted or crisped when dry, erect-patent to squarrose, rarely undulate when moist, lingulate, triangular, ovate, linear-lanceolate, oblong-lanceolate or lanceolate, very rarely orbicular, sometimes keeled, concave or not, decurrent or not at base; lamina uni- or bistratose irregular or regularly, green, yellowish green, yellow, reddish orange or red with KOH; apex rounded, obtuse, acute or acuminate, sometimes cucullate, subulate or apiculate, deciduous or not, occasionally swollen; margins entire or papillose-crenulate, sometimes sinuose or erose, rarely denticulate, recurved at lower third, middle, upper third or up to the apex of the leaf, rarely plane or revolute, uni- to tetrastratose. Costa ending below the apex, percurrent or excurrent, occasionally spurred above midleaf; ventral cells of the costa, in the upper middle of the leaf, quadrate to elongated, smooth or papillose, with or without a band of translucent cells just below the apex, dorsal cells of the costa, in the upper middle of the leaf, quadrate to rectangular, rarely elongated, smooth or papillose; in transverse section at leaf base semicircular, elliptical or rounded; with 2–10 guide cells in 1–2(3) layers, 0–4 layers of ventral stereids, 0–4 layers of dorsal stereids, with or without hydroids, ventral epidermis differentiated or not, bulging or not, papillose or smooth, dorsal epidermis differentiated or not, papillose or smooth. Upper and middle laminal cells rounded, subquadrate, quadrate, oval, hexagonal or rectangular, oblate or not, rarely sinuose, with 1–6 papillae per cell, sometimes low, simple or bifurcate, generally thick-walled; basal cells quadrate to rectangular, very rarely sinuose, differentiated or not, chlorophyllose or hyaline, smooth or papillose, thin- or thick-walled, rarely pitted; marginal basal cells very rarely differentiated. Gemmae multicellular, rarely unicellular, borne in masses in the axils of the leaves, on branched rhizoids in the axils of the leaves or very rarely, on the ventral side of the costa, spherical, ovoid or elliptical, green brown or brown, smooth. Dioicous. Perigonia terminal, perigonial leaves generally concave, smaller and wider than vegetative leaves. Perichaetia terminal on main branches or on short lateral branches, perichaetial leaves similar to vegetative leaves. Seta yellowish to reddish brown, spirally twisted to left throughout, occasionally twisted to right in the upper part. Capsule stegocarpous, erect or lightly inclined, cylindrical, oblong, ovoid or elliptical, brown or red. Annulus generally revoluble or deciduous in pieces, composed of 1–3 rows of hexagonal cells, usually vesiculose. Peristome of 32 or 16 teeth grouped in pairs, very rarely rudimentary or absent, filiform, papillose, straight or spirally twisted, sometimes cleft or perforated, yellow to reddish brown, basal membrane absent or more rarely differentiated. Operculum rostrate to long rostrate, sometimes rostelate. Calyptra cucullate. Spores smooth or papillose, brown-yellowish, green-yellowish or brown.