12. Hygrohypnum ochraceum (Turner ex Wilson) Loeske, Moosfl. Harz. 321. 1903.
Hypnum ochraceum Turner ex Wilson, Bryol. Brit., 400, plate 58 [lower right]. 1855; Calliergon ochraceum (Turner ex Wilson) Kindberg; Hygrohypnella ochracea (Turner ex Wilson) Ignatov & Ignatova; Hygrohypnum ochraceum var. filiforme (Limpricht) J. J. Amann; H. ochraceum var. flaccidum (Milde) J. J. Amann; H. ochraceum var. uncinatum (Milde) Loeske
Plants soft or coarse, bright shiny yellow-green, dull yellow-green, bright or dull green, dull olive green with or without rusty mottling, dirty brown, or rarely blackish green. Stems to 15 cm, usually leafy throughout or with shredded bases or denuded in older extremities, unbranched or irregularly branched; hyalodermis as one epidermal layer enclosing cortex, cells inflated, walls thin, hyaline, central strand well developed. Leaves variable among plants, individual stems, or branches, loosely imbricate or spreading, straight or falcate when dry or moist, ovate-lanceolate, lanceolate, infrequently ovate, or rarely broadly ovate, concave, (0.7-)1-1.8 (-2.5) × (0.2-)0.5-0.8(-1.2) mm; margins erect, entire, minutely denticulate to serrulate in apex; apex acute to long-tapering acuminate, obtuse, or blunt; costa variable, usually double and long with one or both arms reaching mid leaf or beyond, almost ecostate, double and short, single to mid leaf or beyond, or single with 1-3 lateral forks; alar cells variable, quadrate, short-rectangular, or sometimes linear, , region not distinct, irregular; basal laminal cells variable, usually wider, variously shorter, longer, or similar to medial cells, ; medial cells fusiform to linear, long-flexuose, (30-)37-83(-120) × (4-)5-6(-8) µm; apical cells shorter; marginal cells shorter toward apex. Sexual condition dioicous; perichaetial inner leaves long-tapering lanceolate, . Seta reddish brown, 1.6-3.1 cm. Capsule with endostome cilia 1-3.
Irrigated acidic rock and wood in streams; moderate to high elevations (200-3700 m); Greenland; Alta., B.C., N.B., Nfld. and Labr., N.S., Ont., Que., Yukon; Alaska, Ariz., Calif., Colo., Conn., Idaho, Maine, Md., Mass., Mich., Mont., N.H., N.J., Oreg., Pa., R.I., Utah, Vt., Va., Wash., W.Va., Wyo.; Europe; Asia; Atlantic Islands (Iceland).
Hygrohypnum ochraceum is highly polymorphic; it varies from compact specimens with falcate-secund leaves to those with long, trailing stems with straight, widely spaced leaves. Unifying such plants is their dioicous sexuality and present stem hyalodermis. The basalmost laminal cell is generally quadrate or very short-rectangular while those beyond grade to longer rectangular to almost linear. Hygrohypnum ochraceum has often been confused with H. luridum, which differs in being autoicous and a calcicole, lacking a hyalodermis, and having a well-developed group of quadrate to short-rectangular or irregular alar cells.