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Ptychomitrium Fürnrohr, 1829.

The genus Ptychomitrium is not easily confused with any other local moss. It usually has sporophytes, and the polysetous condition will usually be obvious. The calyptra of Ptychomitrium is distinctive: strongly plicate and basally fringed, campanulate and sheathing most of the capsule.

Key to Ptychomitrium Etc.

The mosses keyed in this section are costate acrocarps with strongly crispate leaves. We have in California only one described species, and this has strongly dentate leaves. Its sporophytes are typically polysetous (with more than one sporophyte emerging from a perichaetium). Our species is almost always petricolous on both acid and alkaline rocks.

Species included are all in Ptychomitriaceae:
Campylostelium saxicola (Weber & D. Mohr) Bruch & W. P. Schimper, not known from CA
Ptychomitrium gardneri Lesquereux
Ptychomitrium serratum (C. Müller Hal.) Bruch & W. P. Schimper ex Bescherelle, not known from CA
Ptychomitrium sinense (Mitten) A. Jaeger, not known from CA

Species determination of a Ptychomitrium requires inspection of the larger and more distally placed leaves on a stem. The dentate margin of more proximally placed leaves is often reduced relative to the more distal leaves. Leaf cross-sections are important in species distinction, and these too are best obtained from larger leaves on distal portions of the stems. Cross-sections should be made from areas of the leaf immediately above the shoulders.

An additional genus in the family Ptychomitriaceae may eventually be found in the state. Campylostelium, a moss of higher elevations in such more northern areas as Washington State, has the basally fringed calyptra of Ptychomitrium but that calyptra is not plicate and it covers only the strongly rostrate operculum. It is much smaller than our species of Ptychomitrium, and its capsule is placed on a cygneous seta.

The shape and size of the marginal teeth are specially important in Ptychomitrium. Species differ in number of cells within each tooth; in being sharply pointed or blunt; and in having the teeth upwardly oriented to incurved versus outwardly spreading.

A. Leaf margins entire, plane to erect; leaves ovate-lanceolate without significant differentiation of a narrowed acumen .....Ptychomitrium sinense not known from CA
A. Leaf margins dentate, recurved at least near base; leaves lanceolate but contracted below the middle into a well-defined acumen .....B

B. Marginal teeth of distal 1/4 of leaf sharply pointed and diverging from margin at more than a 30 degree angle; mid-leaf cross-section unistratose except for a narrowly bistratose margin; leaf with a well demarcated acumen that includes about 1/2 or more of that leaf .....Ptychomitrium gardneri
B. Marginal teeth of leaf mostly rather blunt or pointed but inflexed relative to margin; mid-leaf cross-section various; acumen markedly shorter .....C

C. Leaf mostly bistratose above the middle; basal cells rectangular but with lateral walls not sinuose; marginal teeth variable with some of them somewhat sharply pointed and inflexed in plane of leaf ..... Ptychomitrium species A
C. Leaf mostly unistratose; rectangular basal cells with lateral walls sinuose; marginal teeth uniformly blunt .....Ptychomitrium serratum not known from CA

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