Oligotrichum Lamarck & A. P. de Candolle, 1805.

The combination of the leaves crispate and with photosynthetic lamellae will recall Atrichum and especially Pogonatum contortum. Oligotrichum differs from the former in having elimbate leaves, and it differs from the latter in being markedly smaller (less than 5 cm tall). It is easily distinguished from Pogonatum contortum in that the latter will never have abaxial teeth on the laminal surface, nor will it have a wavy appearance to the adaxial lamellae (in adaxial, macroscopic view).
see key to Atrichum Etc.

Species included in this key are all in Polytrichaceae
Oligotrichum aligerum Mitten, not known from CA
Oligotrichum hercynicum (Hedwig) Lamarck & A. P. de Candolle
Oligotrichum parallelum (Mitten) Kindberg, not known from CA

Three members of this genus grow on wet soil banks through much of Oregon and more northern regions; and Oligotrichum aligerum can even be found in southern Mexico. The genus has been encountered in California only once, O. hercynicum near Mammoth.

A. Leaves ovate to oblong, broadest at or above the middle; leaf base not prominently sheathing; lamellae few, confined to the costa that is not distally expanded .....Oligotrichum parallelum not known from CA
A. Leaves lanceolate from a sheathing base; lamellae more than 10, arising from a broadened costa and sometimes from the lamina .....B

B. Leaves with prominent lamellae on both the adaxial and the abaxial surfaces .....Oligotrichum aligerum not known from CA
B. Leaves with lamellae restricted to the adaxial surface .....Oligotrichum hercynicum