Bruchiaceae Schimp.

Plants small, probably annual, gregarious on soil. Stems unbranched or sparsely branched by innovation. Leaves often sheathing, ovate to lanceolate or subulate from a ± oblong base, entire or serrulate; laminal cells of upper leaf (including subula) subquadrate to rectangular to oblong-linear, firm-walled, smooth or prorate abaxially; laminal cells of leaf base similar or longer and thinner-walled; alar cells not differentiated. Costa well-developed, ending near apex or excurrent, often filling subula (if present). Brood bodies not known.

Autoicous or dioicous. Setae very short to elongate, terminal; capsules erect or curved, immersed to long-exserted, obovoid to pyriform with a broad or narrow elongate neck, either cleistocarpous (in Bruchia) or opening by a functional operculum (in Trematodon). Peristome (if present) single, of 16 entire, perforate, or forked teeth, striate below. Operculum (if present) long-rostrate from a conic base. Calyptra mitrate or cucullate, not hairy, smooth or papillose. Spores rather large, mostly subreniform, variably ornamented.

The Bruchiaceae were treated as a subfamily (Trematodontoideae) of the Dicranaceae with three genera (Bruchia, Trematodon, and Wilsoniella) by Brotherus (1924). Crum (1994) took a narrow view of the family (including only Bruchia and Trematodon) and outlined his belief that these two genera represented a sporophyte reduction series "from operculate with peristome well-developed, rudimentary, or lacking in Trematodon to inoperculate and eperistomate in Bruchia and from seta and neck elongate to relatively short in Trematodon and very short in Bruchia." Crum also presented arguments for placing genera sometimes placed here (Eobruchia and Pringleella) outside the family. Goffinet et al. (2009) presented a broader view of the family that included Bruchia and Trematodon as well as three additional and small genera of limited distributions (Pringleella, Eobruchia, and Cladophascum) in the family. The above description does not consider those lesser known genera. Only the widespread but predominantly southern hemisphere Trematodon occurs in N.Z. Trematodon is distinguished from the cleistocarpous Bruchia (which is recorded from mainland Australia by Scott & Stone (1976)) by having capsules with differentiated opercula, usually cucullate calyptra, exserted and long and slender capsules with necks that equal or exceed their urn in length, and variably developed peristomes.