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

Plants in flat patches, olive green. Stems to 3 cm. Stem leaves ovate lanceolate from an ovate base, 2.5--3.5 × 0.6--0.7 mm, both margins plane, intermarginal bands 2--4(--5) stratose, awn to 1 mm, not decurrent, narrowly attached, acuminate, costa narrow proximally, distal laminal cells 2--3-stratose, oblate to rectangular, thick-walled; medial laminal cells quadrate, slightly sinuose, thick-walled; basal juxtacostal laminal cells short- to long-rectangular, sinuouse, thick lateral-walled, dense; basal marginal laminal cells quadrate to short-rectangular, sinuose, thick lateral-walled, not hyaline. Perichaetial leaves enlarged. Seta straight to slightly curved, to 3.5 mm. Capsule occasionally present, exserted, pale yellow, ovoid, exothecial cells oblong, thin-walled, stomates absent, annulus of 1--2 rows, quadrate, thick-walled, operculum short straight, peristome fully developed, not perforate, not split. Calyptra cucullate.

Humid to dry areas, exposed granite, metamorphic, and metavolcanics and basalt, montane woodlands; 670--1400 m; Calif.

Grimmia serrana is endemic to western North America, having been collected only in California, where it is currently known from “localities along the western slope of the Sierra Nevada and two occurrences in the northern Coast Range” (J. Muñoz et al. 2002). Despite its limited distribution, H. C. Greven (2003) found it to be quite common in the area. With its thick, concave leaves, with plane margins and flat costa, Grimmia serrana is best placed in the subg. Litoneuron. This is further supported by a number of other features shared by, but not unique to, all members of this subgenus including a well-developed stem central strand, dioicous sexuality, and long-exserted capsule with a multi-layered, thick-walled annulus. Grimmia serrana is most readily identified by a prominent, multi-layered band of cells that run along the laminal margin distally and become submarginal proximally. This inflated band of marginal cells is unique to this species and readily separates it from all other members of Litoneuron. As stated by J. Muñoz et al. (2002), G. serrana is most likely to be confused with G. ovalis. Both are robust species with ovate-lanceolate leaves from an ovate base. However, the prominent intermarginal bands of G. serrana will readily separate these species.