Atrichum undulatum (Hedw.) P. Beauv. - Common Smoothcap Moss


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Atrichum undulatum - (image 1 of 5)



Family: Polytrichaceae


Rich, humic soil in moist shaded habitats.






Plants 1.5-7 cm high. Leaves undulate, toothed at back,  4.5-9.5 mm long, oblong-lanceolate or rarely oblong-elliptic, acute, more or less keeled at the tip; lamellae 4-6, nearly straight, 2-5 cells high, obscuring less than half of the upper third of the leaf; upper cells 18-30 μm wide. Setae 1.4-4 cm long, clustered in groups of 2 or rarely 1 to 3; capsules 3.5-6 mm long; calyptra toothed with short-bristles at the tip.


The generic name Atrichum refers to the lack of long hairs covering the calyptra, unlike mosses in the genus Polytrichum (haircap mosses).

According to the Flora of North America, this species was introduced from Europe. They consider what Crum refers to as var. altecristatum Renauld & Cardot to be a separate, seemingly native species, Atrichum altecristatum (Renauld & Cardot) B.B. Smyth & L.C.D. Smyth. Whatever the proper taxon, it is said to have twice the chromosome number of A. undulatum and to occur in wet places, with lamellae 4-6 cells high and long, narrow, somewhat curved and inclined capsules more than 5 mm long.


Crum, H. 2004. Mosses of the Great Lakes Forest, 4th ed.

The University of Michigan Herbarium. Ann Arbor, MI


Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols.  New York and Oxford.




Michael Hough 2010