Tomentypnum Loeske, 1911.

Tomentypnum, along with other strongly plicate, costate pleurocarps, has traditionally been placed in a broadly construed Homalothecium (Brachytheciaceae). The recent work of Hedenäs, however, requires placement in the Campyliaceae along with a large number of other aquatic and semiaquatic mosses. In the Campyliaceae, Tomentypnum joins Conardia as one of the two local mosses that produce rhizoids from cells along the abaxial face of the costa. The rhizoids of Tomentypnum are so regularly present as to allow the use of that character as a main diagnostic feature. The much smaller plant Conardia only occasionally has rhizoids inserted on its costa, and this latter genus has papillose rhizoids compared with the smooth rhizoids of Tomentypnum. The feature of rhizoids inserted on the costa should be distinguished from that of nematogons on distal portions of leaves (a common feature of many other Campyliaceae). When it is stated that nematogons are present on leaves, we are referring to rhizoid initials in the leaf lamina itself rather than on the surface of the costa. Tomentypnum, not yet known from the state, should be found in bogs and fens of calcareous areas such as the Marble Mountains of northwestern California.
see key to Homalothecium Etc.

Species included:
Tomentypnum nitens (Hedwig) Loeske