Stout perennial to 2.5 m, simple to the infl; lvs mostly flat, lanceolate, acute to rounded at base; infl to 5 dm, the several ascending branches mostly subtended by reduced lvs; mature pedicels obscurely jointed near the base; valves subrotund, 5-8 mm, about as wide, basally broadly truncate; grains 3, narrowly lance-acuminate, half as long as the valve, the base distinctly above the base of the valve; 2n=60, 160. Swamps and shallow water; Nf. and Que. to N.D., s. to N.J., Ind., and Nebr. (R. brittanicus, misapplied)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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