Tetraphis Hedwig, 1801.

Tetraphis are costate acrocarps with entire and plane-margined, almost orbicular leaves. The sporophytes are exserted on a straight or abruptly angular seta, and the capsules have only four triangular and rigidly erect peristome teeth. Older stems and leaves of Tetraphis have a brick-red wash completely recognizable once the field worker is properly introduced.

Key to Tetraphis

In California, Tetraphis is a moss almost never found on any substrate except logs and stumps, and it seems restricted to the northwestern portion of the state. Its erect stems are usually crowned by a closely arranged series of reduced leaves that form a cup in which are found a cluster of elliptical gemmae. A novice might confuse this gemmae cluster of Tetraphis with that of Aulacomnium androgynum, also found on decaying wood, but usually on drier and more exposed wood. The easy differentiation is that Tetraphis has the gemma cluster subtended by the cup of modified leaves, whereas the gemma cluster of Aulacomnium is without a subtending cup. One should also note possible confusion of these gemma cups with the splash-cup perigonia of such groups of plants as the Polytrichaceae, Philonotis, and Pohlia. The perigonia will show recognizable club-shaped antheridia at all stages of development – features radically different from the elliptical gemmae of Tetraphis.

Species included in this key in Tetraphidaceae:
Tetraphis geniculata Girgensohn ex Milde, not known from CA
Tetraphis pellucida Hedwig

A. Seta smooth and erect; plant common on logs and stumps throughout moist areas of the state .....Tetraphis pellucida
A. Seta bent at about its middle with obvious papillosity at least at that bend; plant very rarely encountered but growing in habitats similar to the previous species .....Tetraphis geniculata not known from CA