Pseudostereodon procerrimus (Molendo) Fleischer
Plants robust, usually regularly and densely pinnate, suberect to procumbent, 2--8 cm, rusty brown to golden brown or occasionally dark green; branches 0.1--1.5 cm, mostly equal. Stems yellowish to brownish, with central strand, pseudoparaphyllia foliose, blunt, weakly toothed. Leaves of stem falcate-secund, ovate-oblong, gradually narrowing to a tapering acumen, margins plane and entire to sinuate, 1--1.5 × 0.5--0.8 mm, often auriculate at base, costa slender, double or absent, median cells linear-flexuose, 60 × 8 µm, somewhat pitted, cells of leaf base slender, yellowish or brownish, porose; alar cells forming a well-defined group in auriculate portion, subquadrate to subquadrate to hexagonal, 7--8 cells high along margin, and forming a triangular group of 6--8 cells in width. Sexual condition dioicous. Sporophytes unknown.
Terrestrial, usually in calcareous open terrain, often on rock, especially cliff ledges and bases, also tundra, open spruce forests and edges of sandy beaches; 0--1500 m; Alta., B.C., Nfld., N.W.T., Nunavut, Yukon; Alaska, Mont.; Europe (south to the Caucasus).
Hypnum procerrimum shows an interrupted distribution in Arctic and alpine areas of the northern hemisphere, usually found in well-drained sites. It is a very distinctive species; some small forms might be confused with Ctenidium molluscum, but the toothed leaves and the leaf cells often with projecting upper ends separate the latter.