1. R. cymòsa, Nutt. Culm triangular; leaves linear (¼´ wide); cymes corymbose, the spikelets crowded and clustered; achene round-obovate, twice the length of the bristles, four times the length of the depressed-conical tubercle.—Low grounds, Penn. and N. J. to Fla., west to N. Ind. and Ill.
2. R. Torreyàna, Gray. (Pl. 4, figs. 1–5.) Culm nearly terete, slender; leaves bristle-form; cymes panicled, somewhat loose, the spikelets mostly pedicelled; achene oblong-obovate, longer than the bristles, thrice the length of the broad compressed-conical tubercle.—Swamps; pine-barrens of N. J. to S. C.
3. R. inexpánsa, Vahl. Culm triangular, slender; leaves narrowly linear; spikelets spindle-shaped, mostly pedicelled, in drooping panicles; achene oblong, half the length of the slender bristles, twice the length of the triangular-subulate tubercle.—Low grounds, Va. to Ga.
[*][*] Achene smooth and even.
[+] Bristles 6, long and conspicuous, upwardly denticulate.
4. R. fúsca, Roem. & Schultes. Culm 6–12´ high; leaves bristle-form channelled; spikelets ovate-oblong, few, clustered in 1–3 loose heads (dark chestnut-color); achene obovate, half the length of the bristles, equalling the triangular-sword-shaped acute tubercle, which is rough serrulate on the margins.—Low grounds, N. Brunswick to N. J., west to L. Superior. (Eu.)
5. R. gracilénta, Gray. Culms very slender, 1–2° high; leaves narrowly linear; spikelets ovoid, in 2–4 small clusters, the lateral long-peduncled; achene ovoid, rather shorter than the bristles, about the length of the flat awl-shaped tubercle.—Low grounds, southern N. Y. and N. J. to Fla.
6. R. oligántha, Gray. Culm and leaves filiform, 6–12´ high; spikelets very few (1–4), ovate-oblong; bristles plumose below the middle; achene obovate-oblong, bearing a conical tubercle {1/3} its length.—Del. (Canby) to Fla.
[+][+] Bristles none, or 1–3 and minute; spikelets pale, 1-flowered.
7. R. pállida, M. A. Curtis. Culm (1–2° high) acutely triangular; leaves and spikelets as in the next species, but only a terminal dense cluster, which is less white or turns pale reddish-tawny; achene obovate-lenticular, tipped with a minute depressed and apiculate tubercle; the delicate bristles 4–5 times shorter or obsolete.—Bogs in pine-barrens of N. J. and N. C.