Trichostomum is a widespread genus of 116 small to moderate-sized species (Crosby et al. 2000). Typically the genus has stems with a hyalodermis and central strand; narrow leaves that are erect to appressed at base and incurved contorted above when dry; distinctly different upper and basal leaf cells with the basal leaf cells usually thin-walled; costa that is stoutly excurrent into a smooth mucro, has guide cells, two well-developed stereid bands, and enlarged, papillose ventral surface cells. The leaf margins in Trichostomum can be plane, erect, or distinctly incurved above, and although most species lack a border of hyaline cells that run up the basal margins, the feature is at times weakly present. Most species of Trichostomum have 16, short, erect peristome teeth on a low basal membrane.

The genus is close to Weissia, Pseudosymblepharis, and Tortella. All four have similarly shaped leaves, costae with two stereid bands, and lax, thin-walled basal leaf cells. In addition, the peristomes found in Weissia, Pseudosymblepharis, and Trichostomum are essentially the same. Weissia differs from Trichostomum only in having more strongly involute leaf margins and a generally smaller size. These two features, however, hardly serve to distinguish the two genera since Trichostomum has some Weissia-sized species as well as species with involute leaf margins. Pseudosymblepharis differs from Trichostomum in having narrower, crispate leaves that are often strongly clasping at base. There are, however, some species of Pseudosymblepharis  with erect-appressed leaf bases similar to those seen in Trichostomum. Tortella differs from Trichostomum in typically having better developed peristome teeth that are spirally twisted and borne on well-developed basal membrane (but there are some gymnostomus as well as cleistocarpous species of Tortella) and in having a very strong basal leaf border of hyaline cells that run up the margins in a v-shaped pattern. The last of these features, however, is weakly expressed in some species of Trichostomum.

The genus Oxystegus is sometimes segregated from Trichostomum (See Stoneburner 1985, p. 294, Norris & Koponen 1989, Zander 1994a) on the basis of such features as the absence of a peristomial basal membrane, fragile leaves, plain upper leaf laminae, broadly sheathing leaf bases with the basal leaf cells running up the margins in a v-shaped pattern, and distinct cellular areolation at the leaf shoulders. It is difficult to maintain these two genera when they are considered on a world rather than regional level because such a treatment results in the unnatural separation of clearly related species (Crum & Anderson 1981). According to Zander (1993) “... Oxystegus cannot be maintained at the world level because of considerable variation in expression and combination of characters among the species.”