A taxonomic revision of Grimmia subgenus Orthogrimmia (Musci, Grimmiaceae)

Grimmia subg. Orthogrimmia comprises nine species distributed on mountain chains or high latitudes mainly in the Northern Hemisphere. This subgenus is defined by the following combination of characters: leaves V-shaped in transverse section, margins flat (seldom recurved in G. reflexidens), proximal marginal cells with the transverse walls thicker than the longitudinal walls, setae erect and straight (curved only in G. arenaria), and capsules symmetric and smooth. I recognize two sections: sect. Donnianae, including G. arenaria Hampe, G. donniana Sm., and G. triformis Carestia & De Not.; and sect. Montanae, comprising G. alpestris (F. Weber & D. Mohr) Schleich., G. caespiticia (Brid.) Jur., G. montana Bruch & Schimp., G. nivalis Kindb., G. reflexidens Mull. Hal., and G. ungeri Jur. Grimmia brachyphylla. Cardot, considered by other authors to be synonymous with G. montana, is shown to be conspecific with Coscinodon humilis, and is here lectotypified. Grimmia sinensianodon is considered to be synonymous with Coscinodon cribrosus, and not with G. caespiticia, as previously believed. All taxa are keyed and described, and typified where indicated. Illustrations and distribution maps are provided for each species.