Herb, perennial, dioecious, caespitose, forming large dense clumps to 0.5 m across; cluster and sand-binding roots present. Culms crowded, erect, terete, 50–100 cm long, 1.0–1.5 mm diam., green, striate, glabrous, simple or occasionally branched; internodes numerous. Sheaths closely appressed, oblong, subulate, 1.0–2.3 cm long, scarious, glabrous, striate; ligule an erect membranous ridge 0.3 mm long formed by the apical margins joining adaxially; lamina caducous, 0.6–1.5 cm long. Spikelets terminal on culms or on long slender pedicels, 1–3 on each culm. Male and female spikelets similar, 1–2.8 cm long, 0.5–0.7 cm wide; males narrow-elliptic, acute, not glossy; females ovoid to globular; glumes ovate, 4–8 mm long; obtuse, minutely ciliate on lower margin, rigid and very dark brown or black apically; males with c. 20 fertile glumes; females 9–20 fertile glossy glumes. Flowers: very shortly pedicellate, dorsiventrally flattened; tepals lanceolate, brown-hyaline. Male flowers: outer tepals 4.0–4.5 mm long; inner tepals 3.2–4.2 mm long; filaments 5–6 mm long; anthers 2.5–3.2 mm long; pistillode minute. Female flowers: outer tepals 6.0–7.5 mm long; inner tepals 4.5–6.0 mm long; staminodes 3, well-developed, c. 1.5 mm long; style branches 2, connate at the base, stigmatic almost to the base. Capsule 1.5–2.0 mm long. Seeds broad-ellipsoid, with longitudinally elongated cells with sinuous walls. Culm anatomy: epidermis with greatly enlarged tanniniferous cells opposite outer vascular bundles, with some of these enlarged cells extending partly through the chlorenchyma but others extend to (and interrupt) the parenchyma sheath, the two types of enlarged cells mostly alternating around the perimeter of the culm cross-section; chlorenchyma of 1 layer of elongated peg cells; pillar and protective cells absent, central cavity present.
Seasonally inundated heaths and swamps, in peaty sand or clay, often in standing water; sites wet most of the year.
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