21a. Eleocharis tenuis (Willdenow) Schultes var. tenuis
Rhizomes 0.4–1 mm thick, soft to hard, longer internodes (2–)5–10 mm, scales seldom decaying to fibers. Culms to 0.35 mm wide. Leaves: distal leaf sheaths with or without apical tooth to 0.2 mm. Flowers: perianth bristles sometimes present. Achenes lemon yellow, stramineous, or yellow-green, finely rugulose and usually finely cancellate at 10–20X, with 8–12 (often obscure) depressions in each vertical series. Tubercles as high as wide or sometimes greatly depressed. 2n = 24.
Fruiting summer. Freshwater shores, wet woods, bogs, ditches; 10–1100 m; N.B., N.S., P.E.I., Que.; Calif., Conn., Del., Ky., La., Maine, Md., Mass., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Vt., Va., W.Va.
Occasionally plants of Eleocharis tenuis var. tenuis are found mostly submerged.