10. Eleocharis quadrangulata (Michx.) Roem. & Schult.

Pl. 73 c, d; Map 283

E. quadrangulata var. crassior Fernald

Plants perennial, usually with relatively stout rhizomes, forming coarse clumps. Aerial stems 40–120 cm long, 2–6 mm wide, sharply (3–)4-angled, lacking cross-lines. Basal sheaths loose, membranous, the lowest ones sometimes enlarged and nearly free from the stem, light brown to brown, less commonly pale green or purplish tinged, the tip strongly oblique, long-tapered to a sharp point on 1 side, sometimes the lowest ones with an elongate, strap-shaped, pointed tip. Spikelets 15–50 mm long, about as wide as the aerial stems, linear in outline, the tips bluntly pointed to pointed, with usually 1 sterile, basal scale. Scales 5–6 mm long, papery, oblong-elliptic to oval in outline, the tips broadly rounded to bluntly pointed, the surface with fine longitudinal lines, straw-colored, the margins lighter, irregularly scarious. Perianth bristles 3–6, rarely none, slender, soft, of unequal lengths, somewhat shorter than to longer than the fruit, very finely retrorsely barbed. Stigmas 2 or 3. Fruits with the main body 2–3 mm long, broadly obovate in outline, biconvex in cross-section, narrowed to an urn-shaped neck at the tip, the surface with a fine network of horizontally elongate cells in 22–28 vertical series, shiny, golden yellow to brown at maturity. Tubercles 0.8–1.4 mm long, flattened, narrowly triangular. June–October.

Scattered in the southern half of the state, mostly in the Ozark Division (eastern U.S. and adjacent Canada west to Texas, south to Mexico). Margins of ponds, lakes, and streams, sometimes in shallow water, rarely submerged in deeper water.

This easily recognized species is unusual among Missouri spike rushes in its coarse, sharply quadrangular stems, persistent spikelet scales (in other species except the related E. equisetoides, the scales are shed from the spikelet base as the fruits mature), and in its dark tubercles (also present in E. equisetoides). It is easily distinguished from E. equisetoides by the lack of septations and quadrangular stems. It also tends to grow at the water’s edge and is only rarely encountered as a submerged aquatic. Eleocharis quadrangulata is an adaptable species and is frequently encountered in disturbed, muddy areas along the margins of cattle ponds.