Thuidium Bruch & W. P. Schimper, 1852.

Thuidium is common and species-rich in the eastern United States as well as in most of the Northern Hemisphere. Its absence from western North America is nearly complete except for an arc of distribution that extends from eastern North America into the high Arctic thence southward in the mountains of Alaska and British Columbia barely reaching Washington State. The stems of Thuidium recognitum are several times pinnately branched and have dense, branched, filamentous paraphyllia. As such, Thuidium could be confused only with Hylocomium splendens. Thuidium differs from the latter species in many respects and can be differentiated immediately by experienced persons. Objective differences include the single costa of Thuidium (not double and branching from the base) and the central papillosity (not prorate).
see key to Hylocomium Etc.

Species included:
Thuidium recognitum (Hedwig) Lindberg, not known from CA