K. Norsk Vid. Selsk. Skrift. 1914(1): 112. 1915. -- Dicranum falcatum Hedw., Spec. Musc. 150. 32 f. 1–7. 1801. -- Arctoa falcata (Hedw.) Loeske, Stud. Morph. Syst. Laubm. 86. 1910.
Plants in rather dense, lustreless, dark green to olive green tufts or cushions, to 20 mm high. Leaves strongly falcate secund, little changed moist or dry, grooved distally but not sharply keeled, not fragile. Larger stem leaves to 4 mm long, with an ovate to obovate, sheathing base which more or less gradually contracts to a linear and setaceous acumen comprising up to 4/5 of total leaf. Lamina cells of leaf limb in up to 10 rows, quadrate to short rectangular, to 8 µm wide, prorate-papillose to mammillose, especially near leaf apex. Median cells of sheathing base smooth, to 8 µm wide, less than 10: 1, in regular rows, rectangular, pitted on lateral walls. Marginal cells of leaf base not differentiated. Alar cells moderately to rather sharply demarcated, not extending to costa, quadrate to rectangular brownish, to 15 µm wide, somewhat inflated and thin walled. Costa diffuse near base, becoming well demarcated in the distal 1/2 of the expanded leaf base, excurrent and occupying nearly all of the distal portion of the awn. Costa cross-section homogeneous, with walls only moderately thickened. Margin plane to erect, entire below but bluntly serrate near apex. Rhizoids red-brown, to 12 µm wide at base, smooth, sparsely produced and restricted to the stem base. Stem cross-section nearly homogeneous but with a poorly defined central strand, with even the outer cortical cells rather large, but somewhat pigmented.
Autoicous with perigonia axillary very near the base of the perichaetium. Perichaetial leaves loosely sheathing only the base of the seta, larger than but otherwise similar to the adjacent vegetative leaves. Monosetous with the seta to 10 mm, yellow to brownish, straight and smooth. Urn to 2 mm long, inclined and arcuate, about 2: 1, wrinkled to somewhat sulcate when dry, strumose. Operculum rostrate, about 2/3 as long as the urn. Exothecial cells to 20 µm wide, to 2.5: 1, regular in size and shape, in vertical rows, short rectangular, rather thick walled. Exothecial cells near mouth of capsule isodiametric and reduced in size, in 2–3 rows; these cells continuing on operculum but abruptly differentiated on beak into much elongated cells. Annulus in several rows of thin walled, quadrate and persistent cells near capsule mouth. Peristome red-brown, inserted near capsule mouth, erect when dry, to 500 µm long, bifid nearly to middle, lanceolate but with the distal portion of each division filiform and hyaline. Dorsal plates of peristome vertically striate but ventral plates and peristome apex sharply papillose. Spores spherical, minutely papillose, to 14 µm.