Brachydontium F├╝rnrohr, 1827.

Brachydontium with its close relative Seligeria, is one of the smallest acrocarpous mosses, usually becoming visible only when one looks across the edge of the rocks on which it is growing. Both species are so small that they are unlikely to be collected unless they have sporophytes.
see key to Seligeria Etc.

Species included:
Brachydontium olympicum (Britton) McIntosh & Spence, not known from CA
Brachydontium trichodes (Weber) Milde, not known from CA