Dicranum Hedwig, 1801.

The alar region in Dicranum is bistratose in all the members of the narrowly defined genus (Orthodicranum and Blindia lack such a bistratose region). The costa within the narrowly defined genus is consistently strong, often excurrent, and there are two stereid bands in at least the proximal half of the costa. Like other members of the Dicranaceae, Dicranum tends to have plane to incurved leaf margins, and its leaves configure themselves in either a keeled or subtubular fashion; they are never completely flat. In California, Dicranum is mostly restricted to the northwest quarter of the state.

Key to Dicranum Etc.

The plants included in this section are large acrocarpous mosses with strongly falcate subulate leaves and short to long median laminal cells. The alar region is a sharply demarcated zone of inflated pale to reddish-brown cells.

Species included in this key are in Dicranaceae, except Blindia (Seligeriaceae):
Blindia acuta (Hedwig) Bruch & W. P. Schimper
Dicranum fragilifolium Lindberg, not known from CA
Dicranum fuscescens Turner
Dicranum howellii Renauld & Cardot
Dicranum majus Turner, not known from CA
Dicranum pallidisetum Ireland, not known from CA
Dicranum polysetum Swartz, not known from CA
Dicranum rhabdocarpum Sullivant, not known from CA
Dicranum scoparium Hedwig
Dicranum spadiceum J. E. Zetterstedt, not known from CA
Dicranum sulcatum Kindberg in Macoun
Dicranum undulatum Schrader ex Bridel
Orthodicranum tauricum (Sapehin) Smirnova

Among the unusual features of taxonomic use in Dicranum is the nature of the distal portion of the leaf on an intact specimen. Leaves are said to be keeled or cylindric-inrolled. The two sides of the leaf lamina describe an acute angle in a keeled leaf; they together describe a semicircle in a cylindric-inrolled moss. The amount of pitting of a cell is of great importance in the distinguishing of species of Dicranum. Cells that are pitted are thick-walled but have areas, often near their distal or proximal ends that are significantly thinner walled.

2008 KEY, P. Wilson

A. Leaf, when dry, rigidly erect, and usually with the majority of the apices broken off and functioning as propagules .....B
A. Leaf apices not caducous .....C

B. Costal cross-section with obvious guide cells but with only a single layer of cells adaxial to those guide cells; capsule erect on a straight seta .....Orthodicranum: O. tauricum
B. Costal cross-section with more than one layer of cells adaxial to the guide cells, these sometimes substereidal; capsule arcuate .....Dicranum fragilifolium not known from CA

C. Alar cells in an auriculate base (often left on stem with careless dissection); margin nearly entire; median laminal cells 6-10:1, not pitted; stereids in costa lacking .....Blindia: B. acuta
C. Alar region not auriculate; margin serrulate to dentate .....D

D. Median leaf cells elongate and strongly porose; costa ridged or toothed dorsally at least near the leaf apex; leaves usually somewhat falcate .....E
D. Median leaf cells nearly isodiametric, not porose; costa not ridged on abaxial surface (though in some cases prorate) .....J

E. Leaf lamina strongly undulate; leaves of dry plant spreading with apex of leafy stem not hamate; margin recurved near the base .....Dicranum polysetum not known from CA
E. Leaf lamina not, or only lightly undulate; leaves of dry plant erect with the leafy stem apex thus markedly hamate; margin plane to erect .....F

F. Abaxial surface of the costa with ridges or teeth in distal 1/3 .....G
F. Abaxial surface of the costa smooth throughout .....I

G. Costa at mid-leaf with two rows of guide cells; leaves mostly about 10 mm long; leaf lamina near the apex with bistratose streaks that are often abaxially dentate .....Dicranum majus not known from CA
G. Costa at mid-leaf with only a single row of guide cells; leaves about 5-8 mm long; leaf lamina unistratose except in alar region .....H

H. Innermost parachaetial leaf said to be gradually acuminate, the point of inflection having a tangent of ~45 degree relative to the longitudinal axis; alar region with rectangular, inflated cells throughout, only gradually transitting to the rectangular cells of the mid-leaf; costa with inconspicuous dorsal ridges .....Dicranum howellii
H. Innermost parachaetial leaf very abruptly tapered to what is essentially a subulate acumen, the point of inflection having a tangent of nearly 90 degree perpendicular to long axis; alar region distally bounded by a row of quadrate, inflated cells that set off that alar region from the rectangular cells of the mid-leaf; costa with dorsal ridges partly more than one cell high .....Dicranum scoparium

I. Costa excurrent; cells of distal portion of leaf heteromorphic in size and shape even in a single leaf .....Dicranum spadiceum not known from CA
I. Costa ending slightly before leaf apex; cells of distal portion of leaf rectangular and similar one to another .....Dicranum rhabdocarpum not known from CA

J. Leaves of moist plants transversely undulate, not crispate .....Dicranum undulatum
J. Leaves not transversely undulate; crispate when dry .....K

K. Leaf bluntly keeled to subtubular in distal portion of leaf with the cross-section at mid-leaf describing a "U"; distal portion of costa without stereid bands; capsules yellow-green to brown; most older leaves broken toward their apices .....Dicranum pallidisetum not known from CA
K. Leaf keeled along costa from at least the middle to near the apex with the cross-section at mid-leaf describing a "V"; distal portion of costa with stereid bands; capsules brown to reddish-brown; leaves seldom broken .....L

L. Both stereid bands of median costa about 4 cells thick; costa long excurrent; leaf base inserted on stem at 60-75 angle and then abruptly ascending and crispate; laminal cells in awn 2-3:1 and prorate with prorulae as long as the cell width .....Dicranum sulcatum
L. Both stereid bands of median costa about 2 cells thick; costa percurrent to short excurrent; leaf ascending throughout with base inserted at less than a 45 angle; laminal cells in awn mostly isodiametric with the prorulae smaller .....Dicranum fuscescens