Tortella (Lindberg) Limpricht, 1888, nomen conservandum.

In California, this is one of the easiest genera of the Pottiaceae to recognize. Our three species are rather large mosses in compact cushions. In California, two of our Tortella have undistorted and fragile leaves; the other has leaves so crispate that they seem to tangle with one another. Under the microscope, the hyaline and rectangular cells of the leaf base ascend up the leaf margin in such a well demarcated zone as to create a V-shaped line between the cells of the base and those of the limb. Our species of Tortella are primarily calciphiles, and the scarcity of such habitats in montane California accounts for the few collections of species of this genus.

Key to Torella Etc.

These are densely papillose acrocarpous plants with plane leaf margins and with strongly differentiated basal cells, usually thin-walled and rectangular. The basal cells extend up the leaf margin so that such thin-walled and rectangular, smooth cells border the actual shoulder of the leaf.

Species included in this key are all in Pottiaceae:
Oxystegus tenuirostris (W. J. Hooker & Taylor) A. J. E. Smith
Tortella alpicola Dixon
Tortella fragilis (W. J. Hooker & Wilson in Drummond) Limpricht
Tortella tortuosa (Hedwig) Limpricht

A. Leaves gradually contracted into a narrowly linear to subulate apex .....Tortella tortuosa
A. Leaves broader at the apex with the costa mucronate .....B

B. Leaves strongly crispate when dry, often losing portions of their lamina but not with broken apices; differentiated basal cells extending barely to the shoulders and thus not defining a V-shaped line between the basal cells and those of the limb .....Oxystegus: O. tenuirostris
B. Leaves rigid, usually with many of the apices broken; differentiated basal cells extending above the shoulders and thus defining a V-shaped line between the basal cells and those of the limb .....C

C. Leaf bases strictly hyaline, without a yellowish blush; distal portion of leaves segmented into a series of elliptical and multicellular segments; leafy stems with rhizoids not formed into a dense indumentum; stems with central strand .....Tortella alpicola
C. Leaf base usually with a yellowish blush; distal portion of leaves not articulated but instead breaking into segments of irregular lengths; leafy stems with rhizoids often densely compacted into axillary indumenta; stem without central strand .....Tortella fragilis