Plants in pendent streamers or in dense mats, green to yellow-green, sparingly branched. Primary stems (stolons) short and prostrate with secondary stems to 40 cm long, prostrate to pendent. Leaves to 3.5 mm, 3–6:1, asymmetric, complanate; undulate, ovate-lanceolate, acuminate to a very narrow apex, loosely imbricate when dry and little changed when moist; Margins plane, not decurrent, serrulate to serrate above the middle, sharply dentate with many recurved teeth at apex. Median cells smooth, 5–8 µm wide, 5–10:1, thick-walled with lumen/wall ratio to 2–4:1, but not very pitted. Alar cells little differentiated or with a patch of thin-walled, nearly isodiametric cells in the cordate base. Median basal cells more elongate, thick-walled (lumen/wall ratio 1–2:1) and pitted. Apical cells little differentiated. Costa short and double. Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Axillary hairs 5-celled, to 180 µm with two basal brown cells, not offset from leaf insertion. Rhizoids brown, 6–8 µm, smooth, inserted on stem immediately below abaxial costal insertion.
Dioicous with male plants similar to females. Perigonia on main axis or terminal on short lateral branches. Perichaetia on main axis, to 6 mm long in an acicular cluster, strongly convolute around the seta. Lower perichaetial bracts ovate, abruptly contracted to acuminate, reflexed apex. Upper perichaetial bracts to 4 mm, abruptly acuminate from a long ligulate base, cells long rectangular, to 15:1. Seta 4–5 mm long, short-exserted. Capsule brown, curved and inclined, not distorted or sulcate when dry, somewhat strangulate at mouth. Urn to 2.0 mm, about 2–3:1. Exothecial cells isodiametric, hexagonal, to 35 µm wide, thin-walled, stomata restricted to neck. Operculum short-rostrate, about 1/3 as long as urn. Exostome smooth to low papillose, light-brown. Endostome segments smooth, open on keel, narrow, about as long as exostome with basal membrane less than 1/4 of total length. Cilia absent. Spores papillose, 18–20 µm.
Neckera douglasii is endemic to the humid coastal forests of northwestern United States. It is almost exclusively an epiphyte on trees close to the coast. No other California moss combines ecostate and strongly undulate, complanate leaves with strongly dentate leaf margins.
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