Tetrodontium Schwägrichen, 1824.

Tetrodontium usually grows in dimly lit positions on the ceilings of rock overhangs. It is very small, and it grows as scattered plants rather than as a monospecific turf. In general the only fully developed leaves are the perichaetial bracts, and much of the photosynthesis is done by thallose flaps of protonematal origin. The capsules on these extremely small plants are diagnostic: four erect, cellular peristome teeth, and a lightly plicate calyptra.
see key to Seligeria Etc.

Species included:
Tetrodontium brownianum (Dickson) Schwägrichen, not known from CA
Tetrodontium repandum (Funck in Sturm) Schwägrichen, not known from CA

A. Perichaetial leaves costate to above middle, ovate and shortly acuminate, protonematal flaps to 2 mm long; flagelliform shoots present .....Tetrodontium brownianum not known from CA
A. Perichaetial leaves ligulate; ecostate; protonematal flaps to 0.5 mm long; flagelliform shoots frequent .....Tetrodontium repandum not known from CA