Plagiothecium sylvaticum var. squarrosum Kindberg
Plants dark green to yellowish green, dull or glossy, in thin to dense mats. Stems to 50 × 1--4 mm, prostrate, rarely erect, complanate-foliate or sometimes julaceous. Leaves usually imbricate, rarely secund with some apices pointing toward substratum, flat to concave, usually asymmetric, 1.5--4 × 0.5--2 mm, oblong-ovate or ovate-lanceolate, acute to acuminate, rarely narrowly obtuse, margins broadly recurved nearly to apex or sometimes plane, serrulate at extreme apex, rarely entire; costa short and double, one branch sometimes reaching the leaf middle, or costa rarely lacking; leaf cells smooth, walls of basal cells with a few pits, rarely pitted to leaf middle; median cells 70--180 × 12--21 μm; decurrent alar region often auriculate and oval in outline, consisting of 3--8 vertical rows of spherical, oval, quadrate, and rectangular cells, 19--80 × 19--29 μm, usually terminating at the base in several spherical or oval cells, sometimes alar region triangular in outline, composed of quadrate and rectangular cells, terminating at the base in a single cell. Specialized asexual reproduction by propagula often present, 72--178 × 9--24 μm, consisting of 3--7 cells. Sexual condition autoicous, sometimes dioicous, often fruiting. Seta light brown to red, often curved, 1.5--3.5 cm long. Capsule light brown to orange-brown when mature, cernuous and arcuate, rarely nearly straight and erect or inclined, 1.5--3.5 × 0.5--1 mm, when dry, strongly contracted below mouth, striate or sometimes wrinkled, rarely smooth, strongly wrinkled at neck; operculum short-rostrate, 0.7--1 mm; cilia 2--3. Spores 9--13 μm.
Capsules mature summer. Woods on rotten logs, stumps, bases of trees, or on humus or soil frequently overlying boulders and cliffs; 50--2740 m; Greenland; Alta., B.C., Man., N.B., Nfld., N.W.T., Nun., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mo., Mont., Nev., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Oreg., Pa., R.I., Tenn., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Europe; Asia; Africa.
This is one of the most common and one of the most variable species of Plagiothecium in North America. The plants have complanate stems to 50 mm, mainly flattened, asymmetric, acute leaves, 1.5--4 mm, with broadly recurved margins, decurrencies that are often auriculate, composed of inflated, quadrate or spherical cells, median cells 12--21 μm wide, capsules 1.5--3.5 mm, inclined to horizontal, slightly curved, and urns distinctly striate when dry. Sometimes, especially in western North America, the stems are julaceous, to about 3 cm, the leaves are strongly concave, nearly symmetric, narrowly obtuse, 1.5--2 mm, and the capsules are almost straight and erect. Plagiothecium denticulatum has been reported for Australia and New Zealand but an examination of the specimens from those regions revealed that they are another species, P. novae-seelandiae Brotherus (R. R. Ireland 1992).