Scirpus atrovirens Willd.

Cespitose perennial to 1.5 m from short tough rhizomes; main lvs to 18 mm wide, mostly on the lower half of the stem, the lower sheaths and blades usually septate-nodulose; infl open or sometimes very compact, once or usually twice widely branched, often with axillary bulblets; spikelets ovoid or short-cylindric, 2–8 mm, all densely crowded in subglobose heads; scales 1.4–2.1 mm, broadly elliptic or obovate, brownish or blackish, the pale midvein prolonged into a mucro less than 0.4 mm; bristles mostly 6, shorter to slightly longer than the achene, ± straight, the upper 2/3 retrorsely barbellate; style trifid; achene very pale to white, compressed-trigonous, 0.8–1.2 mm; 2n=50, 52, 54, 56. Swamps and wet meadows; Nf. and Que. to Wash., s. to Ga., Tex., and Ariz. Fr June, July. Most of our plants belong to the highly variable var. atrovirens, as described above. (S. ancistrochaetus, with the bristles barbellate nearly to the base; S. flaccidifolius, local in se. Va. and adj. N.C., with lax stems, the infls lopping over toward the ground; S. georgianus, with 0–3 short bristles; S. hattorianus, with lower blades and sheaths nearly smooth) Westward, mainly w. of Mississippi R., var. atrovirens passes into var. pallidus Britton, with fewer and larger glomerules and more consistently blackish scales 1.8–2.8 mm, the midrib excurrent into an awn-point 0.4–0.7 mm. (S. pallidus)