Plants in loose or dense, dark-green to red-brown or blackish tufts, dull or occasionally with a metallic sheen. Stem densely foliate, 5--10 (--20) mm high, central strand strong. Cauline leaves concave when moist, to 1.5--2(--2.5) mm, oblong-spatulate to obovate, occasionally with multicellular teeth in distal 1/4, rounded to rounded obtuse at the apex, sometimes apiculate; costa stout, prominent on back, smooth on the abaxial surface to occasionally roughened at the apex, hydroids absent; laminal cells near insertion short-rectangular, 2--4:1, firm-walled, pale and brownish or hyaline, cells 8--10(--12) μm wide, in longitudinal and oblique rows, thin to thick-walled, bulging-mamillose on the adaxial surface, plane on the abaxial. Sexual condition dioicous. Seta 6--7 mm, reddish to yellow-brown with age. Capsule erect, 1.5--3 mm, narrowly cylindric from an indistinct neck, annulus well differentiated, red-brown, of vesiculose cells, persistent or deciduous. [Operculum erect, conic-rostrate, 0.6--0.8 mm. Spores 7--10 μm.]

Loosely consolidated sedimentary rocks, soft limestone, rocky riverbanks, streamsides and bluffs in shaded woods; 0--1050 m; Ont.; Ala., Ariz., Ark., [Conn.], Fla., Ga., Ind., Kan., Ky., Md., Mich., Mo., N.J., N.Y., N.C., Ohio, Okla., Penn., Tenn., Tex., Va., Vt., W.Va., Wis.; Mexico; Europe; West Indies, Central and South America; s Asia; Africa in South Africa; Pacific Islands; Australia.

Cells covering the adaxial costal surface in the related genus Plaubelia are rounded and similar to the laminal cells, being small and generally isodiametric; those of Hyophila are rather different from the laminal cells, being somewhat larger and quadrate to short-rectangular. The adaxial costal cells of Plaubelia are more saliently mammillose than Hyophila, but this is not always easy to establish. In the flora the range of Plaubelia is restricted to Florida, whereas that of Hyophila involuta extends from Florida north to Ontario. Smooth leaves of Dichodontium pellucidum without their typical papillae and generally from the northwestern United States may resemble H. involuta, particularly when there are propagula on branched stalks along the stem, but the former species has quadrate, not rounded, laminal cells, marginal teeth extending to near the base of the leaf, broad leaf insertions, and laminal cells bulging on both surfaces, whereas the leaf insertions of H. involuta are nearly 1/2 the width of the distal leaf lamina, and the laminal cells on the abaxial laminal surface are flat. Leaves are broadest at the base in Dichodontium, above the base in Hyophila. Hyophila involuta apparently rarely fruits in the Flora area (one old sporophyte was seen from Ohio; one fruiting specimen from New Jersey was noted by A. J. Grout 1938, vol. 1, part 3).