Plants small to medium-sized, rarely fairly large, forming loose or dense tufts or mats, green, yellowish or olive green to light yellowish or sometimes grayish in the upper part, brown to blackish proximally, not or hoary. Stems prostrate to erect-ascending, (1-)2-4(-7) cm, copiously branched, mostly with short lateral, tuft-like subpinnate branchlets giving the plants a nodose appearance. Leaves loosely imbricate and often secund on drying, erect-spreading to recurved when moist, (1.5-)2-3.4(-3.8) × (0.4-)0.5-0.7(-0.8) mm, keeled in the distal part, narrowly canaliculate basally, piliferous or seldom epilose; hair-point erect, hyaline, capillaceus, flexuose, 0.3-0.7(-1.1) mm, not or slightly decurrent down the leaf margins; margins broadly recurved to revolute on one or both sides for 1/2-3/4 the leaf length, rarely to the apex, 1-stratose throughout, sometimes with 2-stratose patches; costa percurrent, convex abaxially, (50-)60-80(-100) µm wide near the base, (35-)40-55 µm wide distally, 2-3-stratose basally with (2-)3-4(-5) markedly enlarged adaxial cells, 2-3-stratose in the middle with 2-3(-4) large adaxial cells and 2-stratose distally with (1-)2(-3) adaxial cells; laminal cells 1-stratose, smooth or often strongly pseudopapillose; distal and median cells strongly sinuose, rectangular, 20-30 × 9-10 µm, becoming shorter or oblate towards the margins; basal cells elongate to linear, 25-95 × 8-12 µm, with strongly incrassate and porose walls; alar cells not or weakly differentiated; basal marginal cells quadrate to short-rectangular, rarely long-rectangular, esinuose or very seldom sinuose, hyaline or very rarely chlorophyllose, forming pellucid, 1(-2)-seriate border of (5-)10-20(-25) cells, very occasionally not transparent. Innermost perichaetial leaves (4-6), markedly modified, ovate, acuminate, epilose or very seldom piliferous, hyaline to yellowish hyaline in the proximal half, chlorophyllose in the distal half with strongly incrassate cell walls. Seta dark red to reddish brown, (2.5-)4.5-8 mm. Capsule obloid-cylindric to elongate-ovoid, (1.2-)1.5-2 × 0.3-0.6 mm, brown, dull to weakly lustrous; peristome teeth yellow-reddish, 310-350 µm, papillose, irregularly divided nearly to the base into 2 prongs, sometimes only with elongate perforations, without or with a low basal membrane, 10-15 µm high. Operculum conical-rostrate, to 1 mm, with a straight or slanted beak. Spores (10-)12-14(-16) µm.
Acidic rocks, boulders and cliffs, as well as on soil or gravel, often in late snow areas, on stony mossy tundra, stony slopes and granite rock underhangs on talus slopes, mostly in exposed, dry or moist sites; low to high elevations (0-1700 m); Greenland ; B.C., N.B., Nfld. and Labr., N.S., Ont., Que., Yukon; Alaska, Maine, Minn., Mont., N.H., N.J., N.Y., Vt., Wash.; Europe; arctic, temperate Asia.
Bucklandiella microcarpa is a temperate moss, occasionally penetrating into the Arctic. It has a bicentric distribution in North America, being most common and widespread in the eastern part of the continent and less frequent in the west, where it occurs mostly in the Rocky Mountains from the Yukon to Montana. It is principally a Euro-American species, with some scattered records in Siberia. In Europe it shows distinct continental tendencies and is absent from the oceanic western part, including the British Isles.
Bucklandiella microcarpa is an unmistakable species that is at once distinct from other North American congeners by its long, pellucid basal marginal border of esinuose cells and markedly modified innermost perichaetial leaves, with chlorophyllose distal cells having strongly incrassate walls and basal laminal cells that are esinuose and have porose and prominently thickened lateral walls. Also, it is worth noting that the laminal cells are usually pseudopapillose in B. microcarpa and the pseudopapillosity is especially pronounced in the western North American populations.
Bucklandiella microcarpa resembles B. affinis, B. heterosticha, B. sudetica, and B. venusta in leaf shape and in having pilose leaves. The first two species are also similar in having typically 1-stratose leaf margins. In addition to their less well developed or absent basal marginal border, these species differ from B. microcarpa in having broader costae: 80-100 µm versus 60-80 µm in the proximal portion. Bucklandiella sudetica and B. venusta also differ from B. microcarpa in having regularly 2-stratose leaf margins. In Alaska, B. microcarpa is likely to be mistaken with Dryptodon jacuticus (= Grimmia leibergii), which has long-pilose leaves and similar costal anatomy, with 3-4 much enlarged adaxial cells. However, D. jacuticus has 2-stratose leaf margins and subquadrate to short-rectangular laminal cells in the distal part, straight or only slightly flexuose hair-points, and undifferentiated basal marginal cells.