Grimmia americana Bartram, Bryologist. 32: 8. 1929.
Authors: Roxanne I. Hastings & Dr. Henk C. Greven
Plants in hoary tufts, dark green to brown. Stems 0.5--1.5 cm. Stem leaves oblong-ovate to oblong-lanceolate, 1.5--2 × 0.5--0.9 mm, concave, awn to 1 mm; distal laminal cells 2-stratose, marginal cells 2-stratose; medial laminal cells rounded quadrate, slightly thick-walled; basal juxtacostal laminal cells quadrate to short-rectangular, straight, thick-walled; basal marginal laminal cells quadrate to long-rectangular, straight, thick-walled. Sexual condition gonioautoicous. Seta straight to arcuate, 0.6--1 mm. Capsule usually present, exothecial cells thick-walled, annulus of 1--2 rows, quadrate, thin-walled, operculum rostellate, peristome present, fully developed, perforated and split in most distal part, weakly papillose.
Calcareous rock; of conservation concern; around 1600 m; Ariz., Tex.
Grimmia americana is a rare endemic, currently known only from two sites. Until 1999, the species was known only from its type locality in Jeff Davis Co. of western Texas. A second locality was reported by J. Muñoz (1999a) in Arizona. Thus, it is reasonable to expect G. americana to occur also in southern New Mexico. Grimmia americana is recognized as a member of the subg. Gasterogrimmia by its immersed, ventricose capsule, with a short mitrate calyptra and eccentric setae attachment. The overall habit of the species is also similar to the other members of the subgenus. However, its basal laminal cells are thick-walled while other members have thin cell walls. H. A. Crum (1994) implied that G. americana is similar to G. anodon, but the former is readily separated by its fully developed, perforated peristome and thick-walled basal laminal cells. Grimmia poecilostoma, also most commonly found in the American southwest, has a rudimentary peristome, and a large, revoluble annulus.