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Bryologist 76: 273. 1973. -- Tortula bifrons DeNot., Mem. R. Acc. Sc. Torino 40: 305. -- Aloina rigida var. pilifera (B.S.G.) Limpr., Laubm. Deutschl. 1: 637. 1888.

Plants scattered in loose turfs to 0.5 cm high, green to brownish-green, often with a reddish cast, mostly rather glossy. Leaves ascending to weakly spreading when moist, appressed-erect when dry, oblong-lingulate from a somewhat expanded base, bluntly rounded to 2.5 mm long, 2.5–3: 1 (disregarding awn). Awn smooth and terete, abruptly extending from the blunt laminar apex, often exceeding 2/3 of the length of the rest of the leaf. Median laminal cells transversely elongate with rounded, elliptical lumens, 1.5–2: 1, to 18 µm broad, in regular rows obliquely radiating from costa to margin, thick-walled with lumen/wall ratio 0.5–2: 1. Marginal cells not differentiated. Basal cells quadrate to short rectangular to 25 µm broad, 1–1.5: 1, smooth and thin-walled. Costa occupying about 3/4–7/8 of leaf base, abruptly tapering to the hyaline awn. Branched filaments to 8 cells high densely arranged over the broad costa with the individual cells thin-walled, penicellate and isodiametric but with the terminal cell papilliform thickened at apex. Abaxial cells of costa rectangular, to 20 µm, 2–3: 1, smooth, not pitted on lateral walls. Costa cross-section essentially undifferentiated. Margin entire throughout or with a few serrulations near the apex, broadly incurved from the near the base to near the apex. Axillary hairs to 250 µm, to 15 cells long, with no basal brown cells. Rhizoids red-brown, to 50 µm wide at base, smooth and sparingly branched. Stem nearly homogeneous, somewhat bulbose and mostly buried,
   Dioicous. Seta to 10 mm, red-brown, straight, smooth. Capsule erect or almost so, with the urn cylindric but slightly arcuate, to 2.5 mm, 2.5–3: 1. Operculum conic-rostrate, 1/4–1/2 of urn length. Annulus strongly differentiated, falling in fragments. Peristome twisted counter-clockwise in more than a single spiral, pale yellow to almost hyaline, to 0.7 mm long, with basal membrane comprising up to 1/2 its length, densely spiculose-papillose throughout. Exothecial cells to 25 µm wide, rectangular, 2–4: 1; with thin and oblique transverse walls and with rather thick (lumen/wall ratio 3–4: 1) lateral walls. Spores to 18 µm, finely papillose.

Aloina bifrons challenges standardized descriptions because of the difficulty in defining the costa. There are no significantly elongate and thick-walled cells in the costal region. Rather the cells are quite regularly short rectangular and leptodermous in one to several layers. I have defined the costa as that area of rectangular cells occupying most of the leaf breadth and abruptly differentiated from the transversely elongate cells on the leaf periphery. Furthermore, upon initial dissection, A. bifrons appears to have the leaves abruptly expanded in the bases. This is simply a function of the strong incurvature of the distal margins with the result that the planar leaf base appears markedly broader than the leaf middle.

Elevation by latitude plot for Aloina bifrons
   in California

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