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Dichodontium W. P. Schimper, 1856.

All three species of the genus have rather irregular arrangement of the teeth in the distal portion of the leaves.

Key to Dichodontium Etc.

Mosses treated in this section are acrocarpous somewhat crispate plants with the costa subpercurrent to percurrent in a somewhat blunt apex. The leaf margins of dried plants are strongly inrolled, and this inrolling causes those leaves falsely to appear very narrow. This feature makes confusing the distinctions between the narrow-leaved Dichodontium flavescens and the relatively broader-leaved Dichodontium pellucidum. The leaf margins of these two species are recurved, but those of the markedly smaller D. olympicum are plane.

Species included in this key are in Dicranaceae:
Cynodontium strumulosum C. Müller Hal. & Kindberg in Macoun, not known from CA
Dichodontium flavescens (Dickson) Lindberg
Dichodontium olympicum Renauld & Cardot
Dichodontium pellucidum (Hedwig) W. P. Schimper

A. Adaxial costal surface with quadrate cells throughout; leaf margins plane; cells pluripapillose with papillar salients more than 5 µm high; plant typically in zone of melt-water in very high montane areas .....Dichodontium olympicum
A. Adaxial costal surface with rectangular cells in at least the distal portion of leaf; leaf margins usually recurved near the base; cells mammillose or papillose with papillar salients lower .....B

B. Leaves regularly crenulate above, seldom longer than 2 mm; plant of rocky outcrops at high elevations .....Cynodontium: C. strumulosum not known from CA
B. Leaves irregularly serrulate to dentate above, some more than 2 mm long; plant of riverbanks and muddy seepages at many elevations .....C

C. Leaves mostly more than 4:1, contracted gradually from the broad immediate base to the acuminate apex; teeth of upper leaf margin in part composed of a complete cell .....Dichodontium flavescens
C. Leaves about 3-4:1, broadest a few cells above the immediate leaf base and contracted to a broadly acute or obtuse apex; teeth of upper leaf margin seldom as large as a full cell .....Dichodontium pellucidum, these two species are dubiously distinct

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