Ecology. Open Tucuman-Bolivian montane; on sandstone rocks. Elevation. 1400 m. Distribution. Bolivia: Santa Cruz. World range: endemic to the tropical Andes (Peru, Bolivia).
Didymodon humboldtii is similar to D. rigidulus var. rigidulus (Cano et al. 2008) in leaf shape, apex, 2 stereid bands, 1 row of guide cells, and presence of gemmae, but differing by the strongly incurved leaves, plane to slightly recurved margins above midleaf, and rounded to oval distal laminal cells. The type of Barbula humboldtii was collected by Herzog along the sub-Andean range west of Santa Cruz de la Sierra.
Specimens. Santa Cruz: Herzog 3564.