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Plants erect in olive-green to yellow brown tufts or cushions, to 4 cm high. Lower leaves scale-like, loosely appressed and distant; upper leaves oblong lanceolate with acute apices, to 4 mm long, 3–4: 1, erect spreading when moist but somewhat twisted around stem when dry, keeled distally. Median laminal cells isodiametric with rounded lumens, moderately thick walled with some corner thickening, to 10 µm wide, strongly unipapillose on both surfaces. Basal and alar cells similar to median cells or with a few juxtacostal ones short rectangular, usually not at all inflated. Margins recurved from base to above the middle, dentate at least in distal 1/2, decurrent. Costa ending within about ten cells of apex, somewhat flexuose distally. Costa cross-section with two strong stereid bands and a single layer of guide cells, usually with both epidermises well-demarcated. Axillary hairs to 5 cells long, to 150 µm, with one basal brown cell, not offset from leaf insertion. Rhizoids dense at least near base of plant, smooth, red-brown, repeatedly branched, surrounding a macronematal area which is only 1.5–2 times as long as broad. Stem cross-section with a well-defined central strand, leptodermous inner corticals and several layers of strongly pachydermous, red brown outer cortical cells.
    Multicellular gemmae usually present, borne in globose clusters on end of an elongate and naked gemmaphore, flattened and elliptic with pointed ends, mixed with persistent groups of axillary hairs.
    Dioicous with male plants somewhat smaller than females, bearing terminal perigonia. Perichaetia terminal with bracts somewhat smaller than vegetative leaves. Seta yellow to yellow brown, smooth, erect, to 25 mm long. Urn to 2.5 mm long, about 3: 1 when fresh but becoming relatively longer after loss of spores, inclined to almost erect, strongly sulcate, not at all strumose. Operculum short conic. Annulus well-defined, revoluble. Exothecial cells at capsule mouth to 15 µm broad, isodiametric with rounded lumens in up to 8 rows. Exothecial cells at middle of urn rectangular, to 5:1, to 15 µm broad, not in regular rows, very thick walled on ridges of capsule with lumen:wall ratio 0.25–1: 1, thinner walled in valleys of the sulcate capsule. Exostome pale yellow to yellow brown, to 600 µm long, undivided, finely papillose with papillae in close set horizontal rows. Endostome segments arising from a high basal membrane, lightly papillose, about as long as exostome, open along keel with 2–3, nodulose to appendiculate cilia. Calyptra cucullate, smooth. Spores to 10 µm, smooth or nearly so.

This is one of the most common mosses in California. It ranges there from sea level to subalpine areas, and it may be found from the northern to the southern borders of the state. It is especially common on burned stumps in the coastal forests of northern California. It almost always has at least a few gemmae clusters which appear as spherical objects closely spaced at the end of a seta-like naked stem of gametophytic origin (the gametophore). This type of gemma placement is extremely rare among mosses, and no other California moss shows any similar structure. Careless examination may confuse the gemmaphore of Aulacomnium palustre with the splash-cup placement of gemmae in Tetraphis pellucida Hedw. The latter species may appear to have a spherical, terminal cluster of gemmae but that cluster is surrounded by modified, broad leaves, and its stalk is not completely naked of leaves.

Elevation by latitude plot for Aulacomnium androgynum
   in California

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