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

Plants in hoary tufts, brownish green. Stems 0.3--1 cm. Stem leaves ovate to broadly oblong-lanceolate, 1--1.5 × 0.5--0.6 mm, larger towards stem tips, not keeled, frequently plicate in extreme apex, margins plane, incurved above, long-awned, decurrent, costa weak below, broadened and deeply channeled above; distal laminal cells 1-stratose with 2-stratose ridges, in apex entirely 2-stratose; medial laminal cells short-rectangular, sinuose, slightly thick-walled; basal juxtacostal laminal cells rectangular, straight, thin walls; basal marginal laminal cells rectangular, straight, thick transverse and thin lateral walls, hyaline in 3--4 rows. Gemmae clusters of globular, brown, multicellular gemmae abundantly present on the ventral lamina in distal lamina. Sexual condition probably dioicous, gametangia not seen. Capsule unknown.

Volcanics; of conservation concern; 3500 m; Calif.

Grimmia shastae is a rare endemic known only from Mt. Shasta in California. The discovery of this new Grimmia demonstrates that the bryoflora of California is still insufficiently known. It also shows that the state is exceptionally rich in endemic species of Grimmia: G. hamulosa, G. mariniana, G. nevadensis, G. serrana and G. shastae. Because of its abundantly present gemmae on the adaxial surface of the distal lamina, G. shastae is not likely to be confused with any other species of Grimmia. While gemmae are not rare in Grimmia, they are usually produced on leaf tips (G. anomala, G. hartmanii), on the abaxial side of the leaf (G. torquata), or in leaf axils (G. trichophylla, G. muehlenbeckii, G. austro-funalis). In no other Grimmia species are gemmae produced in clusters on the surface of the adaxial lamina at the distal part of the leaf. The gemmae in G. trichophylla and G. austrofunalis may be borne on the abaxial side of the leaf. The position of the species within the genus is not clear. Although leaf form and areolation agree with G. tergestina, sinuose cell walls, characteristic of Grimmia, are only weakly present, and longitudinal plicae, comparable with those in Grimmia caespiticia, are produced in the extreme apex in most distal leaves.