Nova Hedw. 48: 94. 1989. -- Anictangium flaccidum De Not. Mem. R. Acc. Sc. Torino 39: 254. 1836 -- Schistidium pulvinatum (Hedw.) Brid. var. flaccidum (De Not.) De Not., Syll. musc. 279. 1838.
Plants to 1.5 cm high, in brownish-green to somewhat reddened cushions, opaque-green to nearly black below. Leaves lightly imbricate when dry, erect-spreading when moist, somewhat concave and markedly keeled, to 2 mm long with the awn short to absent except on perichaetial leaves, lanceolate and broadened immediately above the base, 3–3.5: 1. Median leaf cells in very regular longitudinal rows, unistratose throughout or with a single row of bistratose cells at the margin, smooth, to 8 µm wide, isodiametric with lumens regular and with distinct corner thickenings. Marginal cells not differentiated but sometimes with basal marginal cells having transverse walls thickened relative to lateral walls. Basal juxtacostal cells rectangular and rather thin-walled, to 3: 1, to 10 µm wide, with lateral walls straight. Cells of alar region to 8 µm wide, quadrate with rounded lumens, with lumen: wall ratio 3–4: 1; little different from more distal laminal cells. Costa filling less than 1/10 of immediate leaf base, not tapered above, percurrent to shortly excurrent. Costa cross-section at leaf middle rounded to elliptic, less than 1.5 times as thick as the adjacent leaf, with 2 cells exposed on adaxial surface and 6–7 cells exposed on abaxial surface. Margin of leaf limb recurved from immediately above leaf base to very near the apex. Awn inconspicuously decurrent (often with only one cell in that decurrency) consistently serrulate marginally and spinose abaxially. Axillary hairs to 125 µm long, with 6–8 short rectangular, thin and vesicular cells, without a basal brown cell. Rhizoids red brown and monopodially branched, to 30 µm wide at base, smooth to finely verruculose. Stem cross-section round without a central strand or with that strand inconspicuous, with stereome only gradually differentiated from the somewhat leptodermous, hyaline inner cortical cells,
Autoicous with perigonia located only a few leaf axils below perichaetia. Perichaetial leaves loosely sheathing capsule, mostly 1.5–2 times as long as adjacent vegetative leaves with awn present even when absent on vegetative leaves. Seta to 0.5 mm long, yellow to pale brown, straight and smooth. Urn immersed, erect, symmetrical and nearly globose when operculate, smooth when dry, to 1.2 mm long, about 1: 1, not strumose. Operculum with only a short apiculus, about 0.1 mm long. Annulus absent or indistinct. Calyptra mitrate, lacerate basally, covering only operculum Peristome mostly so rudimentary as to be ignored, pale-yellow, to 25 µm long, smooth to finely papillose. Suboral exothecial cells thin-walled, transversely elongate, to 35 µm wide, about 0.3: 1. Median exothecial cells very irregular in size and shape, 15–30 µm wide, not in regular vertical rows, quadrate to rectangular 1–3: 1, thin-walled with lumen: wall ratio more than 5: 1. Basal exothecial cells abruptly longer and more thin-walled than median ones. Stomata phaneroporous, restricted to base of urn. Spores smooth to finely verruculose, to 9 µm.