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

Plants in hoary loose cushions, emerald green to black. Stems 0.6--1.2 cm, central strand weak. Stem leaves linear lanceolate to narrowly ovate lanceolate, 1.5--2.1 × 0.5--0.7 mm, keeled, not plicate, margins incurved distally, awn 0.4--0.8 mm, costal transverse section prominent, terete; distal laminal cells 2-stratose, not bulging, marginal cells 2-stratose, not bulging; medial laminal cells quadrate, slightly sinuose, thick-walled; basal juxtacostal laminal cells long-rectangular to linear, sinuose, thick-walled; basal marginal laminal cells quadrate to short-rectangular, straight, thick-walled, hyaline. Perichaetial leaves slightly enlarged. Sexual condition dioicous. Seta straight, to 1 mm. Capsule occasionally present, immersed to emergent, yellow (rarely brown), ovate with open mouth, faintly but distinctly ribbed, exothecial cells rectangular, thick-walled, stomates absent, annulus of 1 row, quadrate, thick-walled, operculum rostellate, with a short obtuse beak, peristome present, but rudimentary, composed of only a few basal cells, sometimes perforated.

Acidic sedimentary and basaltic metavolcanics; of conservation concern; 900--1200 m; Calif.

Grimmia mariniana is a rare endemic, known only from the coastal mountains of central California. If fertile, the immersed capsules with rudimentary peristome teeth will separate G. mariniana from both G. montana and G. alpestris which, while also being dioicous and lacking stomates, have long-exserted capsules with fully developed peristome teeth. Grimmia nevadensis is similar but lacks peristome teeth and has uniformly rectangular, thin-walled basal laminal cells. The faintly ribbed capsules of G. mariniana may not be evident when the capsules are not turgid. Sterile specimens can be separated from G. alpestris by the lack of bulging cells, and the narrow leaf habit. Identifying sterile specimens of G. mariniana from G. montana, is more problematic as both have narrowly ovate-lanceolate leaves, with similar areolation. However, the basal marginal laminal cells of G. mariniana are hyaline while those of G. montana are not. Grimmia mariniana is easily separated from G. arizonae and G. pilifera, two other members of the subgenus, besides G. nevadensis, that have immersed capsules. Sporophytically, both G. arizonae and G. pilifera have abundant stomata, well-developed peristome teeth, and rectangular, thick-walled, multi-layered annuli. Gametophytically the incurved leaf margins of G. mariniana contrasts sharply with the recurved leaf margins of G. arizonae and G. pilifera. G. Sayre (1955) compared G. mariniana with G. anodon. The straight, centrally attached seta and symmetrical capsule usually with rudimentary peristome teeth will serve to separate specimens of G. mariniana from G. anodon. Gametophytically, the long, narrow leaves, with incurved margins and 2-stratose distal laminal cells seperates G. mariniana from G. anodon.