A new moss species from northern California, Grimmia torenii Hastings, is described. The species is gametophytically similar to Grimmia ovalis, but sporophytically resembles Grimmia tergestina. Many specimens of Grimmia torenii have leaves with papillate-mammillae, readily separating the species from both G. ovalis and G. tergestina. Similar to G. tergestina the perichaetial leaves are enlarged, broadly lingulate and almost entirely filmy throughout. However, these leaves are abruptly narrowed distally to a subulate apex and the distal laminal cells are distinctly thicker than in G. tergestina. Unlike G. tergestina, the peristome is composed of disarticulated teeth and these are often fused at the base; further, the operculum has bulging cells. Grimmia tergestina is rejected from North America; all reported specimens are either G. ovalis, G. poecilostoma or G. torenii.