Verh. K. K. Zool.-Bot. Ges. Wien 38(Sitzungsber.): 49. 1888.
Rhizomes 1.5–5 mm diam. Culms sharply trigonous, 0.5–1.5 m × 2–4 mm. Leaves 3–4, basal, smooth; sheath fronts not pinnate-fibrillose; blades 1 or 2, thickly V-shaped in cross-section, to equaling sheath length. Inflorescences 1–2 timesbranched or subcapitate or of 1 spikelet, branches to 4 cm; proximal bract usually erect, trigonous, 2–7 cm. Spikelets 1–35, in clusters or solitary, 5–12 × 3–4 mm; scales straw-colored to orangebrown or midrib greenish, usually clearly lineolate-spotted, ovate, 3–3.5 × 2.5 mm, flanks ribless, midrib proximally spinulose, apex acute to rounded, notch 0.3 mm deep, awn 0.3 mm, sparsely spinulose. Flowers: perianth members 4–6, brown, bristlelike, equaling to less than 1/2 of achene body, retrorsely spinulose; anthers 2 mm; crest short, spinulose; styles 2-fid. Achenes brown, biconvex, ovoid to obovoid, 2–2.5 × 1.5–2 mm; beak 0.1–0.2 mm. 2n = 42.
Phenology: Fruiting summer.
Habitat: Freshwater tidal shores, marshes, dredge spoil
Elevation: 0 m
Introduced; Oreg., Wash., Eurasia
In North America Schoenoplectus triqueter is known only from the tidal Columbia River system (B. W. Lightcap and A. E. Schuyler 1984), where it forms fertile hybrids with S. tabernaemontani [S. ×kuekenthalianus (Junge) D. H. Kent = Scirpus ×scheuchzeri Brugg]. Fertile hybrids between the same species also occur in Europe.