Stems to 2.5 cm, rounded-triangular to rounded-pentagonal in cross section. Leaves ovate, very short-acuminate, 1.3---1.7 mm, spreading when moist, margins entire, decurrent, papillae short-columnar; costa adaxial stereid band absent or weak, guides cells usually 2. Sporophytes not seen.

Roadsides, hillsides, rocky slopes, fields, chaparral; 50--500 m; Calif., Ore. (L. R. Stark 1980).

This species in distinctive in its distal leaf margins sharply crenulate by projecting papillae (but not by projecting cell walls as in D . nigrescens ), and distal medial laminal papillae tall, branching from the base, and centered over each lumen. The leaves are decurrent on the margins, and arranged in 3 distinct rows on the stem---either straight or weakly spiraling in either direction. This rare species is easily confused with Didymodon ferrugineus , which has a rounded-pentagonal stem cross section, leaves in 3--5 rows, leaf margins weakly recurved, leaf cells smaller, and abaxial surface of the costa less papillose. Perigoniate plants have not been found in the range of the flora.