Stems weakly and irregularly 2-pinnate, smooth; paraphyllia 2--3(--5) cells long, cells mostly ca. 2:1, usually only the terminal one papillose. Stem leaves erect-incurved when dry, broadly ovate, 0.3--0.45(--0.55) mm, ± abruptly shortly and broadly acuminate; costa ending about 4/5 the leaf length. Secondary branch leaves erect-incurved when dry, 0.15--0.25 mm, acute; costa ending ca. 3/4 the leaf length, straight, apical portions often covered with quadrate cells and thus projecting as low crests. Perichaetial leaves serrulate above, subentire below. Seta smooth; endostomial cilia 1--2(--3).

Capsules mature Feb.--Aug.(--Oct.). Moist woods, usually growing on rotten logs, but sometimes on rock, especially limestone, and bases of trees; mostly moderate to low altitudes; Ont., N.B.,; Ala., Ark., Conn., Fla., Ga., Ill., Ind., Iowa, La., Md., Me., Mich., Minn., Mo., N.C., N.J., N.Y., Ohio, Pa., S.C., Tenn., Va., W.Va.; Mexico, Central America, n and c South America; West Indies; Europe.

Because of its wide range in eastern North America, this species is often confused with others in the family. In the southernmost part of its North American range, C. involvens may be distinguished by quadrate-celled paraphyllia and a rough seta. Cyrto-hypnum pygmaeum is more delicate with elaborate branching, with leaves (when dry) erect rather than ± incurved, and with papillose branches and stems. Rauiella scita has leaf cells strongly bulging, is more robust and 1-pinnate with larger, quadrate-celled paraphyllia, and has longer acuminate stem leaves. All the true Thuidia have branched paraphyllia and cells papillose only at back. Species of Haplocladium have leaf cells 1-papillose. Similarly, Helodium blandowii has 1-papillose leaf cells and its paraphyllia are branched and long-celled.