Ecology: Montane forest; epiphyte, on living and dead branches. Elevation: 1400-2650 m (Ecuador: 2370-2650 m, Peru: 2000-2050 m, Bolivia: 1400 m). Distribution: Endemic to the tropical Andes.

Acidodontium lanceolatifolium is distinguish by the rather glossy or lustrous, densely tufted plants to 3.5 cm, narrowly oblong-lanceolate leaves to 3 mm, distinctly long acuminate apex, entire to finely crentulate margins above, 1 row of elongate cells forming a indistinct border, smooth, long excurrent costa, hexagonal-rhomboidal upper cells to 13 µm wide, subquadrate basal cells, setae to 22 mm long, erect to inclined clavate capsules to 5 mm long, ± long neck (equal to slightly shorter than urn), and conic operculum.