Serpoleskea subtilis (Hedwig) Loeske
Plants dull, in green to brownish mats; pseudoparaphyllia foliose. Leaves erect-spreading and often subsecund, 0.25--0.5 mm, somewhat narrowed to the insertion, entire or nearly so; distal cells typically elongate, (2--)3--5:1, oblong-rhomboidal; subquadrate alar cells rather numerous but inconspicuous, 6--8 or more along the basal margins. Specialized asexual reproduction absent. Sexual condition autoicous. Perichaetial leaves entire. Seta 7--12 mm. Capsule erect or nearly so, symmetric, 1--1.5 mm, oblong- cylindric, + contracted at the short neck and sometimes also below the mouth when dry; annulus of 1 layer of cells; operculum conic, obliquely short-pointed to rostellate; stomata in the neck; peristome teeth yellow-brown; cilia of endostome 1--2 and rudimentary or lacking. Spores 9--13 µm.
Bark at base of hardwoods, exposed roots, rarely on logs; low to moderate elevations; N.B., N.S., Ont., P.E.I., Que., Yukon; Ariz., Ind., Maine., Mass., Mich., Mo., N.H., N.J., N.Y., N.C., Okla., Va., Vt., Wis.; Europe; Asia.
Especially distinctive features of P. subtilis include the entire leaf margins, elongate distal cells, and fairly numerous subquadrate alar cells. The capsule is erect or nearly so. This is the only species of the genus typically found on bark.