Stems to 2.5[--7] cm, sclerodermis present. Leaves ovate, ligulate, elliptic or short-lanceolate, (0.3--)1--2(--2.5) mm, entire; leaf base usually not differentiated in shape but occasionally widened and ovate; costa ending 1--3 cells below the leaf apex (blunt-leaved plants) or percurrent or short-excurrent as a stout mucro, rounded to semicircular in section at midleaf, guide cells 2--4; distal laminal cells usually subquadrate, occasionally triangular or transversely elongated, 1:1--2; often 2-stratose marginally or in patches medially.

Usually found on limestone, occasionally conglomerate, sandstone, basalt, clay, soil or siliceous rock, cliff faces, gorge walls, boulders, streamsides, seepage and humid places; warm temperate areas to Arctic tundra; 100--1980 m; Greenland; Alta., B.C., Nfld., N.W.T., Nunavut, Ont., Yukon; Alaska, Ark., N.Mex.; Mexico; Central America; South America; Eurasia

The perichaetial leaves reach 1.7 mm, little more than half the length of those of M. hornschuchiana. The phenomenal range of variation in leaf length and shape matches that of Dichodontium pellucidum (Dicranaceae). Because M. sendtneriana has the appearance of a Didymodon, it is important to examine the collection carefully for the distinctive lateral perichaetia (terminal in Didymodon). Both Molendoa sendtneriana and Anoectangium aestivum have the distinctive lateral perichaetia, but large plants of Molendoa sendtneriana have two stereid bands, and small plants have a costa ending below the apex and also often have leaves with 2-stratose portions, features that are absent from Anoectangium aestivum in the range of the flora. The most distal leaves of M. sendtneriana are commonly a deep green and constrast strongly with the tan proximal portions of the turf. The lateral perichaetia, when present, will distinguish this species from Hymenostylium recurvirostrum, which grows commonly on the same substrate; when absent, the commonly elongate distal leaf cells in the leaf midportion and the lack of an adaxial costal epidermis of the latter species (in the range of the flora) are helpful distinguishing traits. When sterile, Gymnostomum aeruginosum is similar to M. sendtnerianum but has smaller laminal papillae, mostly 3--5 per cell, and smaller leaf cells. Often plants of M. sendtneriana are encrusted with a distinctive black substance distally. Variation in leaf size and shape is substantial (see discussion by R. H. Zander 1977); usually the leaf apices of large plants are acute and those of small plants are obtuse.