Barbula Hedwig, 1801.

The several species of Barbula, in the sense in which we view the genus, are, in California, rather uncommon plants of disturbed or semi-desert sites. Most past treatments included in Barbula species that we treat under Didymodon. Barbula differs from Didymodon in rather technical microscopic characters: clear, rather than brown basal cells of the axillary hairs; a well-developed adaxial epidermis on the costa; and more densely papillose cells. Field differentiation can, however, rely upon the density of papillosity that results in an appearance of greater opacity in Barbula. Our local species of Barbula differ from Didymodon in having a smaller length:width ratio of the leaves: typical Barbula has elliptic to ovate or ligulate leaves while those of Didymodon are lanceolate, often narrowly so. The broader leaves of Didymodon may allow confusion with Tortula, and this is reflected in our treatment of Pseudocrossidium, a genus historically segregated from Tortula.

Key to Barbula Etc.

Here we include a group of acrocarpous plants with at least a trace of papillosity, and often with the papillosity obscuring the cell outlines. The leaves are typically broader than those on plants assigned to Didymodon, but they are more narrow than those of Tortula or Syntrichia. Unlike the latter two genera, Barbula, Didymodon and Pseudocrossidium technically have a trace of an adaxial stereid band on well-developed leaves but that stereid band may be elusive on many specimens.

Species included in this key are all in Pottiaceae:
Barbula convoluta Hedwig
Barbula ehrenbergii (Lorentz) Fleischer
Barbula eustegia Cardot & Thériot
Barbula orizabensis C. Müller Hal., not known from CA
Barbula unguiculata Hedwig
Bryoerythrophyllum recurvirostrum (Hedwig) P. C. Chen
Pseudocrossidium crinitum (Schultz) Zander
Pseudocrossidium obtusulum (Lindberg) H. Crum & L. E. Anderson

A. Leaves with hyaline to yellowish awns; juxtalaminal, abaxial cells of the costa surface usually enlarged and yellowish-brown to orange in a pair of uniseriate rows on each side of costa .....Pseudocrossidium: P. crinitum
A. Leaves without hyaline awns; juxtacostal, abaxial cells along distal portion of costa not differentiated .....B

B. Margins of leaves very strongly revolute in one or more spirals; thin walled cells with hollow papillae present within the spiralled margin; abaxial costal epidermis differentiated in cross-sectional view .....Pseudocrossidium: P. obtusulum
B. Margins of leaves not so strongly revolute and differentiated; costa without a differentiated abaxial epidermis .....C

C. Leaf margins recurved almost to leaf apex; costa percurrent to shortly excurrent and mucronate .....D
C. Leaf margins with recurvature restricted to base or sometimes extending nearly to leaf middle; costa various .....E

D. Leaves ovate to ovate-lanceolate, mostly less than 3:1; costa on at least some leaves mucronate in the rather blunt apex; plant green to brownish-green without any reddish blush; margin at leaf apex crenulate papillose but without any trace of toothing; median leaf cells less than 10 µm in diameter .....Barbula orizabensis not known from CA
D. Leaves lanceolate to ligulate-lanceolate; mostly more than 4:1; costa mostly subpercurrent but not mucronate; plant usually with a reddish blush; margin at leaf apex often with enlarged cells giving a hint of toothing; median leaf cells more than 10 µm in diameter .....Bryoerythrophyllum: B recurvirostrum

E. Costa very shortly excurrent in the mucronate apex; median leaf cells so papillose as to obscure the outlines of the cell lumen; plant mostly of disturbed habitats; leaf margins recurved to near apex .....Barbula unguiculata
E. Costa mostly subpercurrent; median cells only lightly and inconspicuously papillose; leaf margins plane, or recurved only in proximal half .....F

F. Costa percurrent in the rounded to obtuse apex; median leaf cells nearly smooth or obscurely papillose; plant of calcareous semiaquatic habitats often associated with tufa deposits .....Barbula ehrenbergii
F. Costa ending before the rounded apex; median leaf cells papillose with lobed papillae which are inserted over the central lumen and thus not obscuring the cell outlines; plant of disturbed areas especially along streams .....G

G. Perichaetial leaves, at least in part, rounded-obtuse or bluntly acute with these leaves convolute-sheathing .....Barbula convoluta
G. Perichaetial leaves acute with the inner ones abruptly contracted to a subulum, these leaves loosely ascending .....Barbula eustegia