Thalli thin, narrow, to 2(-3) mm wide, pale green to yellowish; prostrate, erect, or pendent, bifid, rarely irregularly pinnate. Lamina unistratose, with a narrow midrib and numerous hairs along the margins, and on the ventral surface of the midrib; hairs unicellular, solitary singly or paired, sometimes in groups of 3-5; surface plane to deeply concave with inflexed margins. Midrib 2-8 cells wide, epidermal cells smooth or papillose, larger than the inner cells; central strand absent; oil-bodies absent or very small, homogeneous; wings unbordered. Gametoecia on minute branchlets scattered along the ventral side of the midrib, androecia inside a globose sac, gynoecia hidden under a thullus flap. Sporophytes surrounded by a fleshy calyptra, pseudoperianth lacking; capsules spherical to ovoid, dehiscing in 4 valves. Vegetative reproduction by gemmae or caducous branches.