Trematodon is best recognized by its long-necked capsules. The genus has

undifferentiated alar cells, an autoicious condition (in Central American species), vertically striate outer peristome surface, and subreniform spores. Collections without sporophytes cannot be distinguished from Dicranella or Ditrichum. Trematodon longicollis capsules are twisted at the neck when dry and on hydration move in circles much like those in Campylopus, where the motion is caused by its cygneous setae.

The Bruchiaceae consists of four genera, Bruchia, Eobruchia, Pringleella, and Trematodon, all of which have capsules with long, well-developed, stomatose necks and large, highly ornamented spores (see Buck 1979a). Trematodon differs from the others in having cucullate rather than mitrate calyptrae. Bruchia is the only cleistocarpous genus in the family.

Bruchia queenslandica Stone and Pringleella pleuridioides Card. occur in Mexico and so may be encountered in Central America.  They differ from Trematodon in having mitrate calyptrae and immersed to emergent capsules.  In addition, B. queenslandica has apiculate capsules, while P. pleuridioides is eperistomate.