21b. Eleocharis tenuis (Willdenow) Schultes var. verrucosa (Svenson) Svenson, Rhodora. 41: 66. 1939.
Eleocharis capitata (Linnaeus) R. Brown var. verrucosa Svenson, Rhodora 34: 202, plate 221, figs. 2, 14. 1932; E. verrucosa (Svenson) L. J. Harms
Rhizomes (1–)1.5–2 mm thick, hard, longer internodes 2 mm, scales decaying to fibers. Culms bluntly angled to smooth, seldom deeply sulcate, to 0.5 mm wide. Leaves: distal leaf sheaths without tooth, or rarely with slender apical tooth to 0.2 mm. Flowers: perianth bristles absent. Achenes dark brown, dark green, or yellow, coarsely (to finely) rugose at 10X, usually coarsely cancellate at 10–20X, 6–10 prominent depressions in each vertical series. Tubercles greatly depressed, rarely pyramidal. 2n = 20.
Fruiting summer. Fresh, often calcareous, shores, wet woods, ditches; 10–600 m; Ala., Ark., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mo., Nebr., Okla., Pa., S.Dak., Tenn., Tex., Va., W.Va., Wis.
Occasionally plants of Eleocharis tenuis var. verrucosa are found mostly submerged.
Harms used a chromosome number as a basis for raising Eleocharis tenuis var. verrucosa to a species (L. J. Harms 1972), but he did not correlate chromosomes with morphology, and I have not located any of his voucher specimens. There are too few chromosome number reports for use in defining taxa in the E. tenuis complex (A. E. Schuyler 1977).