Stereodon alpicola Lindberg & Arnell
Plants in thin to dense mats, light- to yellowish green, glossy. Stems to 10 ´ 1 mm, simple or irregularly branched; epidermal layer of stem cells with exterior walls thinner than those of the 1-several layers of interior walled cortical cells. Leaves flaccid, close to somewhat distant, erect-spreading, concave, smooth, 0.3--0.8 ´ 0.1--0.3 mm, ovate-lanceolate, symmetric, gradually acuminate, margins plane to erect, distinctly serrulate; median cells 33--61 ´ 5--9 µm; alar cells differentiated, quadrate to short-rectangular, 14--28 ´ 7--9 µm. Specialized asexual reproduction rarely present, propagules, 28--47 ´ 9--14 µm, composed of 2--5 cells, green to yellowish green, smooth. Sexual condition dioicous. Sporophytes unknown.
Calcareous rocks and cliffs; 3,000 m or above; Nun. (Seymour I.); Alaska (Arctic Village, Point Barrow), Colo. (Summit Co.); Europe.
Isopterygiopsis alpicola is an Arctic-alpine species that is rare or seldom collected. R. Tuomikoski (1939) was apparently the first to note the close relationship of this species to I. pulchella. The shorter, broader leaf cells and the serrulate leaf margins of I. alpicola are the only notable differences distinguishing it from I. pulchella.