Authors: Roxanne I. Hastings & Dr. Henk C. Greven

Plants in loose, not very hoary patches, greyish-green to olive-green. Stems 0.5--2 cm. Stem leaves broadly ovate-lanceolate, from mid leaf gradually narrowed to a short subula, 1.5--2 × 0.7--1 mm, margins plane, occasionally slightly incurved distally, intermarginal bands absent, awn short, denticulate, costa broad proximally; distal laminal cells 2--3-stratose; medial laminal cells irregular rounded, slightly thick-walled; basal juxtacostal laminal cells elongate with nodulose walls; basal marginal laminal cells short-rectangular with thickened transverse walls. Perichaetial leaves not enlarged. Seta straight, 3--3.5 mm. Capsule occasionally present, long-exserted, dark brown, cylindric, exothecial cells isodiametric, thin-walled, stomates present, operculum erect-subulate, peristome perforated in distal half, split in distal half, papillose. Calyptra mitrate.

Shaded dry boulders at forest fringes; of conservation concern; 870--2895 m; Colo., N.Mex.; Mexico; Central America (Guatemala); South America.

Since its description in 1897, G. bernoullii has been a forgotten species. However, in 1997, H. C. Greven found it in Mexico, growing abundantly on boulders near Pico de Orizaba. The species was unknown in the United States until he found one sample of G. bernoullii from Colorado in MICH. In 2003, W. Weber revisited the locality and found the species again. In 2002, Worthington collected G. bernoullii in the Sacramento Mountains of New Mexico. The species is likely to be confused with other members of the subg. Litoneuron, having the habit and growth of G. laevigata, and sporophytes of G. ovalis. It differs, however, from G. laevigata by its short-rectangular basal marginal cells and its elongate, thick-walled basal juxtacostal cells. The awns of Grimmia bernoullii are also much shorter and are narrowly attached, and the long-exserted dark brown capsules have extremely long opercula. Grimmia bernoullii has been confused frequently with G. ovalis. It differs from the latter by imbricate leaves with plane margins, ellipsoid capsule with long-rostrate, straight operculum, and mitriform calyptra.