Limnobium cochleariifolium Venturi in F. Ardissone et al., Erb. Crittog. Ital., ser. 2: no. 453. 1871 (as cochlearifolium); Calliergon goulardii (Schimper) Kindberg; Hygrohypnum smithii var. goulardii (Schimper) Wijk & Margadant; Hypnum goulardii Schimper; Ochyraea cochleariifolia (Venturi) Ignatov & Ignatova

Plants very soft, yellow to yellow-green with conspicuous rusty mottling. Stems to 5 cm, usually shorter, denuded basally, usually unbranched or infrequently and irregularly branched; hyalodermis absent, epidermal cells small, walls thick, similar to subadjacent cortical cells, central strand weak, poorly differentiated. Leaves stiffly and loosely imbricate to erect-spreading, straight, sometimes secund, changing little or shrinking visibly when dry, loosely imbricate or spreading when moist, usually ovate, very broadly ovate, or ovate-elliptic, very deeply concave to cochleariform, (0.5-)0.8-1.2(-1.5) × (0.3-)0.6-1(-1.3) mm; margins recurved in small leaves, usually plane in larger leaves, entire; apex usually obtuse or rounded, rarely acute; costa usually double and short with one arm to mid leaf, sometimes single and short to mid leaf, or ecostate; alar cells few, quadrate, short-rectangular, or irregular, region not clearly defined or undifferentiated; basal laminal cell length variable; medial cells short-fusiform, short linear-flexuose, or rhombic, 26-48(-55) × (4-)5-6(-8) µm; apical cells shorter to more rhombic; marginal cells shorter. Sexual condition unknown; perichaetia unknown. Seta yellowish to reddish, 1.2-1.6 cm. Capsule with endostome cilia 2 or 3.

Acidic rock in irrigated streams, on shaded, irrigated cliffs and boulders; moderate to high elevations (1300- 3700 m); Nunavut, Yukon; Alaska, Colo., Mont.; Europe.

Hygrohypnum cochleariifolium is rare in the flora area and documented by eight examined specimens; these specimens come from the far north or as disjunctions south along the Rocky Mountains to Colorado. The species may be recognized by the following character combination: small leaves, usually less than 1 mm; leaf shape varying from ovate to broadly ovate to ovate-elliptic with generally recurved margins; costa usually short and double; and alar cells essentially undifferentiated. Most distinctive is the leaf concavity; no other species in the genus has leaves so deeply concave. The plants grow in loosely woven, easily fragmenting, often silt-clogged patches or small, tightly woven patches; the leaves may be crowded or very distant, with regularly cucullate apices.