Authors: Roxanne I. Hastings

Plants 7.0--10.0 mm, dark brown green. Stem leaves broadly ovate-lanceolate, 0.9-1.2 ´ 0.4 mm, margins plane, apex plane, awn 0.2--1.0 mm, lamina non-plicate; distal laminal cells 1-stratose; medial laminal cells 1-stratose; juxtacostal basal laminal cells rectangular to long-rectangular, 27--51 ´ 8--12 µm, thin- to thick-walled; marginal basal laminal cells oblate to quadrate, 5--12 ´ 9--12 µm, evenly thick-walled. Sexual condition dioicous. Seta 0.3--0.5 mm. Capsule immersed, cupulate; peristome present, scalloped, xerocastique.

Only known from siliceous or granite-slate outcrops; 1500--1700 m; B.C., Yukon; Alaska.

R. I. Hastings (1999) recently described this species, which is known only from northwestern North America. The specimens were all originally identified as C. cribrosus, which it resembles in its immersed capsules and superficially cribrose peristome teeth. However, C. yukonensis is separated by its xerocastique peristome (i.e., opens when dry) and non-plicate, plane margined, 1-stratose leaves. Additionally, unlike C. cribrosus, the peristome teeth are not perforated, rather the ornamentation has been "scalloped out" down to the cell walls on either side of the teeth. Thus, while superficially appearing perforated, the cell walls are intact. Its leaves resemble those of C. calyptratus but they are much smaller, more broadly ovate, and are never revolute. Additionally it has an immersed capsule and the teeth are scalloped, not solid as in C. calyptratus. The marginal basal laminal cells are oblate to quadrate, unlike any other Coscinodon in North America.