2. Arctoa hyperborea (With.) Bruch & Schimp. in B.S.G. 北方极地藓 bei-fang ji-di xian
Bryol. Eur. 1: 87. (fasc. 33/36 Mon. 3, 2). 1846. Bryum hyperboreum Gunn. ex With., Syst. Arr. Brit. Pl. ed. 4, 2: 811. 1801. Type. Norway.
Plants slender, 1–5 cm high, brownish green, shiny, in dense tufts. Stems erect, simple or forked, radiculose only at the base. Leaves in many rows, 3–5 mm long, erect-patent, upper parts reflexed or secund, narrowed from an oval-lanceolate base to a subulate apex; margins entire or somewhat serrulate only at the apex; costa slender, occupying 1/8–1/6 the leaf base width, ending near the apex or shortly excurrent; leaf cells incrassate throughout, upper cells irregularly rounded-quadrate or short-rectangular, less than 2:1; lower cells slightly elongate; alar cells distinctly differentiated, nearly quadrate to short-rectangular. Setae stout, purple, 5–8 mm long; capsules erect, oblong-obovoid, 1.5 × 1.0 mm, symmetric or nearly so, with 8 striate when dry; annuli developed, and deciduous; opercula obliquely rostrate; peristome teeth not spreading when dry, divided halfway down, often striate. Spores green, ca. 30 µm in diameter, finely papillose.