Hypnum ruthenicum Weinmann
Plants light green with red secondary stems and branches, green or red branchlets, 4--8 cm, erect, frondose-dendroid, in loose to somewhat dense tufts arising from stoloniferous primary stems matted with whitish or reddish-brown, papillose rhizoids. Secondary stems with pinnate and 2-pinnate branches, branches attenuate, 1.5--3.0 cm, branchlets attenuate, 4--7 mm; lamellae apical cells round, elliptic, square, or rectangular in cross-section, branched rhizoids often arising from the top surface, smooth. Stem leaves clasping stem, 3--4 ´ 1.5--2.5 mm, smooth or wrinkled, ovate, apiculate or obtuse to acute, entire, long-decurrent with many hyaline, inflated cells, 1-stratose, margins plane, costa single, weak, smooth, ending near leaf middle, leaf cells smooth or minutely prorulose, cell walls non-pitted or pits not evident, median cells vermicular, 40--81 ´ 5--7 µm; proximal branch leaves similar to stem leaves, smaller, gradually grading distally into leaves similar to branchlet leaves above; median branchlet leaves 0.5--1.0 ´ 0.3--0.5 mm, plicate, ovate to ovate-lanceolate, broadly acute, irregularly and strongly toothed to serrate from apex to leaf middle, serrate to entire proximally, long-decurrent with many hyaline, inflated cells, 1-stratose, margins plane or narrowly recurved near base, costa single, strong, commonly dorsally toothed, ending below apex, leaf cells smooth or minutely prorulose by projecting cell ends, cell walls non-pitted or pits not evident, median cells vermicular, 28--45 ´ 5--7 µm. Sexual condition dioicous; archegonial and antheridial plants similar, perigonial and perichaetial buds on stem near branches; perigonial bracts broadly ovate, acute; perichaetial bracts ovate, acute to acuminate. Seta orange to red, smooth, twisted, ca. 1.5 cm. Capsule red, solitary, ovoid, arcuate, cernuous, smooth, not contracted below mouth, 3 ´ 1 mm; annulus none; operculum not seen, reported as long-conic, almost rostrate; peristome hypnaceous, endostome as long as exostome, cilia lacking. Calyptra cucullate, covering 1/2 capsule. Spores 12--24 µm, sometimes germinating inside capsule.
Humus on ground or logs along creeks and rivers, or other moist, shaded habitats; 15--550 m; w B.C.; w Alaska, nw Wash.; Asia.
This is a distinctive species somewhat reminiscent of Climacium because they both have erect secondary stems arising from a creeping primary stem and the plants occur in wet habitats. Pleuroziopsis is lighter green, more slender in appearance with a frondose-dendroid habit, an ovoid, arcuate, cernuous capsule with a hypnaceous peristome, the teeth with fine cross striolations, compared to the coarser dendroid habit of Climacium that has a cylindric, straight, erect capsule with narrow peristome segments that are densely papillose. Another important feature differentiating Pleuroziopsis from Climacium that was not stressed when the family Pleuroziopsidaceae was described is the nature of branching that distinguishes the two genera and the family Climaciaceae. In Pleuroziopsis, the plants are erect from a creeping primary stem, just as they are in Climacium, but they are also frondose-dendroid, i.e., they are flattened and the secondary and tertiary branches are divided, often several times, so the plants are noticeably frondose. In Climacium, on the other hand, the plants are not flattened but the branches arise around the distal end of the erect, secondary stem and the branches seldom, if ever, produce branchlets. The capsules of the two genera are quite different (R. R. Ireland 1968). However, the value at the familial level is not as important since reduced peristomes are known to occur in some families of pleurocarpous mosses, as M. S. Ignatov et al. (1998) have pointed out for the Brachytheciaceae.