Abstract
The North American endemic moss Dicranum howellii Renauld & Cardot, described in 1888 based on material from Oregon, U.S.A., had yet to be validly typified. A lectotype for D. howellii is designated herein based on one of two potential type specimens in the Renauld collection in PC. Dicranum howellii is currently known from western North America in Canada (British Colombia) and the U.S.A (Alaska, California, Idaho, Montana, Oregon and Washington). Traditionally it has been considered as close to, or a synonym of, Dicranum scoparium Hedw. and specimens of it are frequently confused with the latter species. Dicranum howellii can be distinguished from D. scoparium based on its suddenly narrowed inner perichaetial leaves that end in a long, flexuose point; leaves that are concave below and tubulose above; slightly decurrent leaf bases; in transverse section, leaf cell-walls that are of variable thickness; and the presence of a sulcus on the dorsal side of the costa.
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