14. C. Háspan, L. Culms sharply angled (1–1½° high); leaves linear, often reduced to membranous sheaths; umbel spreading, the filiform rays mostly longer than the 2-leaved involucre; spikelets narrowly linear; scales light reddish-brown, oblong, mucronate, 3-nerved.—Ponds and ditches, Va. to Fla. and Tex.
15. C. dentàtus, Torr. (Pl. 1, fig. 9.) Culms slender (1° high); leaves rigid and keeled; umbel erect, shorter than the 3–4-leaved involucre; scales reddish-brown, with green keel, ovate, acute, 7-nerved.—Sandy swamps, N. Eng. and northern N. Y. to S. C. and W. Va. Spikes often abortive and changed into leafy tufts.
[+][+] Achene linear to oblong; scales appressed, pointless or nearly so.
[++] Perennial by tuberiferous stolons.
16. C. rotúndus, L. (Nut-grass.) Culm slender (½–1½° high), longer than the leaves; umbel simple or slightly compound, about equalling the involucre; the few rays each bearing 4–9 dark chestnut-purple 12–40-flowered acute spikelets (4–9´´ long); scales ovate, closely appressed, nerveless except on the keel.—Sandy fields, Va. to Fla. and Tex.; also adventive near Philadelphia and New York city. (Eu.)
17. C. esculéntus, L. Culm (1–2½° high) equalling the leaves; umbel often compound, 4–7-rayed, much shorter than the long involucre; spikelets numerous, light chestnut or straw-color, acutish, 12–30-flowered (4–7´´ long); scales ovate or ovate-oblong narrowly scarious-margined, nerved, the acutish tips rather loose; achene oblong-obovate. (C. phymatodes, Muhl.)—Low grounds, along rivers, etc., N. Brunswick to Fla., west to Minn, and Tex.; spreading extensively by its small nut-like tubers and becoming a pest in cultivated grounds.
[++][++] Perennial, propagating by corm-like tubers from the base; spikelets narrow, acuminate, often teretish; scales oblong-lanceolate; achene linear-oblong.
18. C. strigòsus, L. Culm mostly stout (1–3° high); most of the rays of the umbel elongated (1–5´), their sheaths 2-bristled; spikelets 5–25-flowered, spreading; scales several-nerved, much longer than the achene.—Damp or fertile soil, Canada to Fla., west to Minn., Tex., and the Pacific. Very variable in the number and length of the rays of the simple or compound umbel, and in the size of the spikelets (2½–6 or even 12´´ long), more or less densely crowded on the axis.
§ 4. DICLÍDIUM. Style 3-cleft; spikelets narrow, terete or nearly so, few–many-flowered, the scales closely appressed and the broad wings of the jointed rhachis enclosing the triangular achene.
19. C. speciòsus, Vahl. Culm stout, mostly low (5–20´ high); rays of the simple or compound umbel mostly all short and crowded; spikelets 10–20-flowered, yellowish-brown at maturity (3–7´´ long), the short joints of its axis winged with very broad scaly margins which embrace the ovate triangular achene; the scales ovate, obtusish, imbricately overlapping. (C. Michauxianus, Gray, Manual; not Schultes.)—Low grounds and sandy banks, N. Eng. to Fla., west to Minn. and Tex.