Plants: small to medium-sized, in open to dense turfs, green, yellow-green, red-green, or red. Stems: 0.5–3(–5) cm, evenly foliate, julaceous or not, often branching; rhizoids few, micronemata present at base of stem, occasionally in clusters along stem, macronemata axillary. Leaves: strongly imbricate when dry, erect when moist, ovate to lanceolate or rarely lingulate or triangular, flat or concave, 1–3 mm; base rarely decurrent; margins plane to strongly revolute, entire to serrulate distally, 1-stratose, limbidium absent or occasionally present; apex obtuse to acuminate; costa percurrent to short-excurrent with awn present, guide cells usually in 1 layer; alar cells not differentiated; laminal areolation heterogeneous; proximal laminal cells abruptly quadrate or rectangular, shorter than more distal cells, 1–2(–3):1; medial and distal cells vermicular to rhomboidal or hexagonal, usually 3–6(–8):1, walls thin to incrassate, rarely porose. : Specialized asexual reproduction by rhizoidal tubers or absent. Sexual: condition dioicous; perigonia and perichaetia terminal; perigonial and perichaetial leaves not much differentiated, outer perichaetial leaves larger, inner leaves smaller than leaves of innovations. Seta: usually single, ± straight or somewhat flexuose. Capsule: inclined or nutant, pyriform to clavate, 2–6 mm; hypophysis slender, not inflated or rugose; operculum convex, apiculate; peristome double; exostome yellowish, teeth well developed, lanceolate; endostome not adherent to exostome, basal membrane high, segments well developed, with ovate perforations, cilia long, appendiculate or sometimes nodose. Spores: shed singly, 10–18(–20) µm, smooth to papillose, yellowish or yellow-brown. Nearly worldwide, except Antarctica, tropical, subtropical, temperate to boreal regions, rare in arctic-alpine climates.
Species ca. 40 (6 in the flora). Species of Imbribryum are relatively large, with elongate, evenly foliate stems and strongly imbricate leaves. The plants commonly grow on soil or rock, often associated with waterfalls, seeps and springs, or splashed rock. The plants have stout setae 1–3 cm in length; the capsules have well-developed peristomes. The genus is especially well represented in the mountains of New Guinea, the Neotropics, southeast Asia, and Africa. Most species produce spheric rhizoidal tubers; the presence of leaf axil bulbils, reported from European material of I. gemmiparum, has not been confirmed for North American collections. Many species are difficult to identify as they are morphologically variable, especially I. alpinum and I. muehlenbeckii. There is one undescribed species in the western United States, discussed under I. alpinum.