1. Triquetrella californica (Lesquereux) Grout, Moss Fl. N. Amer. 3: 201. 1934.
Anomodon californicus Lesquereux, Mem. Calif. Acad. Sci. 1: 30. 1868
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; low to moderate elevations (50-500 m); Calif., Oreg.
Triquetrella californica in distinctive in its distal leaf margins sharply crenulate by projecting papillae (but not by projecting cell walls as in Didymodon 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 flora area.