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Plants
green to dark green, usually with a reddish cast.
Stems
to 2 cm, central strand present.
Stem leaves
often twisted, appressed to weakly spreading or spreading-flexuose when dry, spreading to spreading-recurved and not keeled when moist, monomorphic, lanceolate, grooved adaxially along the costa, especially near leaf apex, 0.8-2.5(-4) mm, base scarcely differentiated to oblong in shape, margins recurved below mid leaf or to above mid leaf, entire, apex acute, not fragile, commonly ending in a conical cell; costa percurrent or more commonly short-excurrent, not strongly spurred, not much widened or tapering, lacking an adaxial pad of cells, adaxial costal cells quadrate to short-rectangular, ca. 4 cells wide at mid leaf, guide cells in 1(-2) layers; basal laminal cells differentiated medially or across the leaf, walls thin to weakly thickened, rectangular or seldom quadrate, not perforated; distal laminal cells 7-10 µm wide, 1:1, nearly smooth or papillae simple or 2-fid, 2-3 per lumen, lumens irregular or oval to rounded-quadrate, walls thin or evenly thickened, convex on both sides of lamina, 1-stratose or occasionally 2-stratose in patches.
Specialized asexual reproduction
very rare, by multicellular gemmae in clusters in leaf axils.
Seta
0.8-1 cm.
Capsule
1.5-2.5 mm; peristome teeth 32, linear, twisted
1
/2 to once, to 1300 µm, occasionally rudimentary or absent.
Spores
9-12 µm.
Distal laminal KOH reaction
light to dark red-brown, occasionally deep red-orange.
Varieties 2 (2 in the flora): North America, Mexico, Central America, South America, Eurasia, n Africa, Atlantic Islands (Iceland), Pacific Islands.
Didymodon vinealis
is often difficult to distinguish from sterile forms of
D. rigidulus
, but the elongate cells commonly found on the adaxial surface of the costa near the boat-shaped leaf apex, the often strongly papillose laminal cells, and the usual presence of a distinct groove down the adaxial surface of the leaf along the costa are characteristic features. Some but not all specimens may be quickly assigned to this taxon by a unique deep slit floored by elongate cells on the adaxial surface of the costal apex (the adaxial epidermis being absent), visible as a clear window abaxially.
Bryoerythrophyllum recurvirostrum
is immediately distinguished by the clear, enlarged proximal cells. Like
Bellibarbula recurva
, small forms of
D. vinealis
may have quadrate or very short-rectangular proximal cells and sinuose costa, but the former has thick-walled proximal cells and the costa twists laterally, not vertically in the concave distal portion of the leaf of
D. vinealis
, and the adaxial cells of the costa of commonly elongate, 2:1 or more.