Arctoa Moss

Arctoa hyperborea is a rare arctic-alpine moss found on rock ledges or crevices at high elevations. It is distinguished from other species of the genus by its short-excurrent costa, shorter seta (the length is highly variable), and peristome not spreading when dry.

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.

Plants in compact, dark green tufts. Stems 1-3(-5) cm. Leaves erect-spreading, lanceolate, subulate, 2-3 mm; costa 30-55 µm wide at base, short-excurrent, rough near tip; distal laminal cells mostly subquadrate (1-2:1), incrassate; basal laminal cells elongate, alar cells differentiated, quadrate or slightly enlarged. Seta 4-6(-8) mm. Capsule exserted, slightly curved, obscurely to distinctly ribbed when dry, annulus developed, separating; peristome large, not spreading outward when dry. Spores 18-30 µm.

Distribution: China, Russia, Europe, and North America.

Habitat: on soil, humus or rocks in forests.

Bryum hyperboreum Gunnerus ex Withering, Syst. Arr. Brit. Pl. ed. 4, 3: 811. 1801; Cynodontium hyperboreum (Gunnerus ex Withering) Hagen; Dicranum hyperboreum (Gunnerus ex Withering) Smith