Authors: Roxanne I. Hastings

Plants 10--15 mm, pale olive green. Stem leaves oval to ovate-lanceolate, 1.1--1.6 ´ 0.3--0.6 mm, margins incurved distally, apex plane, awn 0.1--0.6 mm, lamina 2-plicate, plications never extended to base; distal laminal cells 2- to 3-stratose; medial laminal cells 1-stratose; juxtacostal basal laminal cells rectangular to long-rectangular, 21--55 ´ 9--12 µm, evenly thick-walled; marginal basal laminal cells quadrate to long-rectangular, 12--51 ´ 9--15 µm, thin or thick end walls and thin lateral walls. Sexual condition dioicous. Seta 1.5--1.8 mm. Capsule exserted, cylindrical; peristome present, cribrose, xerocastique.

Shale, slate, and granitic rock in tundra; 980--1700 m; Greenland; Yukon; Alaska.

Coscinodon hartzii is endemic to Arctic regions of North America. Until 1992, this species was known only from its type locality at Scoresby Sound in e Greenland. B. M. Murray (1992) reported collections from Mt. Michelson and the Philip Smith Mountains of Alaska. W. C. Steere's (1978) and J. Muñoz's (1998) citations of C. calyptratus from these sites have turned out to be C. hartzii. A new location in se Yukon suggests that this species may be widespread across northern North America. Coscinodon hartzii is recognized by its weakly 2-plicate leaves coupled with an exserted capsule and cribrose peristome. It commonly also has 3-stratose regions in the distal parts of its stem leaves.