Plants to 20 cm long, in deep green or brownish green to almost golden green wefts, very regularly 3–5 times pinnate with a prostrate main axis, arching-ascending secondary axes and planar tertiary and quaternary branches, usually with annual growth well marked by the production of a single secondary ascending axis and with the next year's growth initiating from the center of that previous years ascending axis. Plants mostly with opposite to sub-opposite branching, not distorted when dry. Leaves of primary ascending axis often rather distantly inserted, to 3 mm, about 3: 1, ovate to ovate lanceolate, abruptly constricted to an undulate acumen. Leaves of ultimate branches concave, ovate-lanceolate, to 0.8 mm long, about 3–4: 1. Margins plane or recurved near base or more strongly recurved on ultimate branchlets, not at all decurrent, serrate to serrulate at base, often sharply dentate near apex. Median cells prorate at both ends, 4–5 µm wide, linear, about 10–15: 1, thick-walled with lumen: wall ratio 2–3: 1, strongly pitted. Median basal cells orange to red-brown, markedly broader and shorter than adjacent, more distal cells, thick-walled with lumen: wall ratio about 1: 1. Alar cells almost not differentiated. Costa double, often asymmetrically inserted on larger leaves with at least one fork reaching about 2/3. Paraphyllia to 300 µm long, 2–3 cells wide at base and once to twice branched with branches paired. Axillary hairs 5-celled, to 250 µm with a very long basal brown cell, not offset from leaf insertion. Stem cross-section without a central strand, without a hyaloderm, with a well marked stereome of pachydermous, pigmented cells, and with inner cortical cells larger but somewhat collenchymatous. Rhizoids closely fascicled and red-brown, very sparingly produced, primarily at tips of ultimate branches which contact the substratum. Rhizoids to 20 µm in diameter at insertion, arising from area immediately lateral to alar cells at leaf insertions, repeatedly branched with segments mostly strongly curved, smooth and rather thick-walled.
Dioicous with male plants similar to females. Perichaetia on ascending axis, about as long as the subtending leaves. Seta to 3 cm long, erect, redddish brown, smooth. Capsule light brown, inclined to pendent, arcuate, neither sulcate nor strangulate. Urn to 2 mm, oblong and asymmetric, about 2: 1. Exothecial cells quadrate to short rectangular, 1–1.5: 1, to 35 µm broad, not in regular rows, with thick lateral walls and thin transverse walls. Stomata phaneroporous, restricted to neck. Annulus present, not revoluble. Operculum conic-rostrate, to 1/4 of urn length. Exostome to 800 µm long, minutely reticulate striate to almost smooth below, papillose above, light-brown. Endostome segments smooth to lightly papillose, perforate along keel, about as long as exostome with basal membrane about 1/2 of total length. Cilia 2–3, nodose. Spores green, smooth to very lightly papillose, to 15 µm.
In cool temperate coniferous forests and arctic tundra throughout most of the Northern Hemisphere, this plant may be contribute more to the biomass than any other bryophyte. It is immediately recognized by the almost candelabra appearance of the extremely regularly pinnate stems. Tamm (1953) studied this moss in one of the most comprehensive studies of any plant in terms of biomass production in relation to habitat. Hylocomium splendens is known from only a single California collection: oak forest along the Smith River near Gasquet. In Oregon, within less than 50 miles of the California border, H. splendens becomes one of the most important mosses.