Donn'S Dry Rock Moss

Grimmia donniana is characterized by a monoicous gametophyte. Female perichaetial leaves are up to 2.5 mm long, with a hyaline lower part and a percurrent costa. Male perigonia are found on short subperichaetial branches, with innermost perigonial leaves 0.8 mm long, ovate, and obtuse or mucronate. The plant forms dense, compact cushions, with erect, branched stems up to 20 mm long. Leaves are elongate-lanceolate, with a narrow base and rounded or obtuse apex, and are concave at the base. The leaf margins are plane, and the basal paracostal cells are elongate-rectangular with smooth walls. The diagnostic feature is the presence of marginal rows of elongate-rectangular, hyaline cells in the leaf base, with evenly thin walls extending to the broadest part of the leaf. The calyptra is mitrate.