Hypnum ruthenicum Weinmann, Bull. Soc. Imp. Naturalistes Moscou 18: 485. 1845; Girgensohnia ruthenica (Weinmann) Kindberg

Plants light green, frondose-dendroid. Stems with primary stems stoloniferous, branches1.5-3 cm, attenuate, branchlets 4-7 mm, attenuate; lamellae with apical cells round, elliptic, square, or rectangular. Stem leaves clasping, ovate, smooth or wrinkled; base long-decurrent, 1-stratose; apex apiculate or obtuse to acute; medial laminal cells vermicular, 40-81 × 5-7µm. Proximal branch leaves gradually grading distally into leaves similar to branchlet leaves; median branchlet leaves plicate; base long-decurrent; margins plane or narrowly recurved near base, serrate to entire proximally, irregularly and strongly toothed to serrate distally; apex broadly acute; medial laminal cells 28-45 × 5-7 µm. Sexual condition dioicous; archegonial and antheridial plants similar, perigonial and perichaetial buds on stem near branches; perigonial leaves broadly ovate, acute; perichaetial leaves ovate, apex acute to acuminate. Seta smooth. Capsule red, not contracted below mouth. Calyptra cucullate, covering 1/2 capsule.

Humus on ground or logs along creeks and rivers, moist, shaded habitats; low to moderate elevations (10-600 m); B.C.; Alaska, Wash.; e Asia.

Pleuroziopsis ruthenica a distinctive species, somewhat reminiscent of Climacium; both have erect secondary stems arising from a creeping primary stem and occur in wet habitats. Pleuroziopsis is lighter green and more slender in appearance, with a frondose-dendroid habit, an ovoid, arcuate, cernuous capsule with a hypnaceous peristome and exostome teeth with fine cross striolations; Climacium has a coarser dendroid habit and a cylindric, straight, erect capsule with narrow, densely papillose endostome segments. Another important feature distinguishing Pleuroziopsis from Climacium is the nature of branching. In Pleuroziopsis, the plants are erect from a creeping primary stem, as in Climacium, but they are also frondose-dendroid, that is, they are flattened and the secondary and tertiary branches are divided, often several times, so the plants are noticeably frondose. In Climacium, the plants are not flattened; the branches arise around the distal end of the erect secondary stem and seldom, if ever, produce branchlets.