Plants small to medium-sized, rather slender but stiff, rarely robust, forming loose or dense cushions, tufts or mats, dull, variable in color, olive or yellowish green, yellowish or orange-brown to olivaceous distally, brown to blackish brown proximally. Stems (0.5-)1.5-4.5(-8) cm tall, erect to ascending, rarely prostrate, usually sparingly branched to almost unbranched. Leaves erect-appressed when dry, erect-patent to spreading when moist, lanceolate to narrowly ovate-lanceolate, broadly canaliculate to carinate, (1.2-)1.5-2.3(-2.8) × 0.4-0.8 mm; margins broadly recurved to 1/2-3/4 the leaf length on one side, narrowly and shortly recurved or plane on the other side, 2(-3)-stratose for 1(-4) cell rows and somewhat bulging to 1-stratose in the distal half; epilose or terminating in a hyaline awn, awns stout, denticulate to crenate, erect to erect-recurved, 0.15-0.4 mm; costa subpercurrent to percurrent, strongly convex on the abaxial surface, in tranverse-section semi-terete, (50-)60-85(-100) µm wide at the base, 40-55 µm wide near the apex, 3(-4)-stratose in the middle and at the base, with 3(-4) enlarged adaxial cells, 2(-3)-stratose with 2-3 adaxial cells distally; laminal cells 1-stratose with occasional 2-stratose strands near the apex, smooth to pseudopapillose; basal laminal cells elongate, (15-)25-50(-55) × 8-10 µm wide, with thickened, sinuose-nodulose lateral walls; alar cells not or only slightly differentiated, usually yellowish; basal marginal laminal cells quadrate to short-rectangular, pellucid, with moderately thickened and mostly sinuose walls, forming an indistinct border of (2-)5-10(-15) cells; medial and distal laminal cells quadrate to short-rectangular, mixed with oblate (5-)10-20(-25) × 5-10(-12) µm. Inner perichaetial leaves ovate-lanceolate, usually pilose. Seta yellow to brown, 2-3.5 mm. Capsule brown, dull to glistening, ovoid, obloid to obloid-cylindric, smooth, (0.7-)1.1-1.6 × 0.4-0.65 mm; operculum conic, with a straight or slanted beak; peristome teeth 280-410 µm, orange-yellow to reddish brown, papillose, usually variously cleft into 2-3 prongs in the distal half or only perforated to undivided, with a low basal membrane, 35-50 µm high. Spores (10-)12-16(-18) µm.
Dry, exposed or sheltered acidic rocks, boulders, cliff ledges, and rocky ground in fellfield habitats, less often in moist places, rock surfaces and in fissures, stony or gravelly ground among boulders and pebbles, well-drained talus slopes and hillsides, sometimes soil; low to high elevations (0-3600 m); Greenland; St. Pierre and Miquelon; Alta., B.C., N.B., Nfld. and Labr., N.S., Que., Sask., Yukon; Alaska, Calif., Colo., Idaho, Maine, Mont., N.H., N.Y., Oreg., Vt., Wash., Wis.; South America (Argentina, Chile); Europe; arctic and temperate Asia; Atlantic Islands (Falkland Islands, Iceland, South Georgia); Australia; Antarctica (South Sandwich Islands, South Orkney Islands, South Shetland Islands, Antarctic Peninsula).
Apart from Bucklandiella microcarpa, B. sudetica is the most common species of the genus in North America. It is highly variable, with a number of morphotypes to which, in the past, taxonomic status was given. Some morphological and anatomical structures exhibit consistency, making B. sudetica a fairly well-defined species, difficult to confuse with others of the genus. It is best characterized by its slender, sparsely branched stems; short and narrow leaves; muticous or short (to 0.4 mm) hyaline awns; leaf margins recurved and 2-stratose distally with frequent 1-stratose patches; relatively narrow costa that is distinctly convex on the abaxial surface and semi-terete in transverse section, 2-3-stratose near the apex, 3-4-layered in the proximal part, with 3-4 enlarged adaxial cells; distal leaf cells tending to be short or very short, quadrate to short-rectangular; and basal laminal cells mostly sinuose-walled to the insertion.
One of the most distinctive phenotypes of Bucklandiella sudetica consists of robust plants with an always strong costa and prominently thickened leaf margins. They are sometimes designated as forma kindbergii (Frisvoll) Ochyra & Bednarek-Ochyra (A. A. Frisvoll 1988; H. Bednarek-Ochyra 1995) and are scattered throughout the southern distribution area of the species growing in the same habitats as typical plants of B. sudetica. They appear to be intermediate between the typical form of the species and B. macounii, and are characterized by being muticous or with short awns, to 0.15 mm; 2-stratose leaf margins for 1-3(-5) cell rows, with occasional 3-4-stratose spots for 1-2 cell rows; and a robust costa, 70-90 µm wide basally, which is sometimes irregular in outline and 3(-4)-stratose in the base and 3(-4)-stratose in the middle. However, on account of the dark green or dark olivaceous color and slender habit of the plants, entirely hyaline awns, leaf margins recurved on both sides, predominantly 3-stratose costa, and strongly pseudopapillose laminal cells, these plants are considered as a variant of B. sudetica. The opposite phenotype of B. sudetica consists of epigean and robust plants with 1-stratose leaf margins, and a narrow (55-85 µm in the base) and thin (2-3-stratose basally) costa. They may be mistaken for B. microcarpa, which, however, is a strongly branched plant with a flexuose awn, prominent pellucid basal marginal borders, and less sinuose cells towards the base of the leaf.