11. Schoenoplectus subterminalis (Torrey) Soják, Cas. Nár. Mus., Odd. Prír. 140: 127. 1972.
Water bulrush, water club-rush, swaying bulrush, scirpe subterminal
Scirpus subterminalis Torrey, Fl. N. Middle United States 1: 47. 1824
Plants mat-forming; rhizomes to 1 mm diam; terminal tubers sometimes present, to 3 mm thick, fleshy. Culms subcylindric, 0.2–1.5 m × 0.5–1 mm. Leaves 3–20+, smooth; sheath fronts sometimes delicately pinnate-fibrillose; blades 3–20, when erect C-shaped in cross section proximally, elliptic most of length, when submerged usually flaccid and filiform to narrowly ribbonlike, probably longer than sheath, 0.2–1 mm wide. Inflorescences a solitary, erect spikelet; proximal bract erect, like stiff leaf blade, 7–60 mm. Spikelets 5–15 × 3–7 mm; scales pale brown, or central region green when young, ovate-lanceolate, 4–6 × 1.5 mm, smooth, margins sometimes ciliolate apically at 40X, midrib obscure, apex acute, entire, minutely mucronate. Flowers: perianth members 6, brown, bristlelike, from 1/2 of to equaling achene beak, spinulose; anthers 2–3.5 mm; styles 3-fid. Achenes brown, strongly trigonous, obovoid to obpyriform, (2.5–)3–3.5 × 1.5–1.7 mm; beak 0.3–0.8 mm. 2n = 72.
Fruiting summer. Submerged to emergent in water to 1 m or sometimes terrestrial, fresh lakes, streams, bogs; 10–2200 m; B.C., N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Calif., Conn., Del., Fla., Ga., Idaho, Ill., Ind., Maine, Md., Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Y., N.C., Ohio, Oreg., Pa., R.I., S.C., Utah, Vt., Va., Wash., Wis.
Schoenoplectus subterminalis often forms lawnlike, underwater mats that are entirely vegetative or have only the inflorescences emergent. This species is probably extirpated from Illinois. Schoenoplectus subterminalis var. terrestris Paine [= S. subterminalis forma terrestris (Paine) Fernald] probably does not deserve taxonomic recognition.