Ecology. Open Yungas montane, possibly extending into the shrubby humid puna; exposed habitats, on wet soil and rocks. Elevation. 2250-3450 m. Distribution. Bolivia: La Paz. World range: widespread, particularly in the Northern Hemisphere.
Didymodon tophaceus is characterized by the oblong-lanceolate to ligulate leaves to 2 mm, obtuse to round apices, broadly decurrent bases, recurved margins (lower ca. 3/4 leaf length), subpercurretn costa, elongate, distal ventral cells of the costa, in cross-section ventral stereid band absent or weakly developed, dorsal stereid band usually distinct, upper lamina cells ± isodiametric with 1-2 low papillae or absent, and firm-walled, rectangular basal cells. This species is usually associated with calcareous rocks, often encrusted with lime. Gyroweisia boliviana R.S. Williams, based on three syntype collections made by Williams in 1901 and 1902, is a synonym.
Specimens. La Paz: Williams 1785, 1786, 2868.