2. Eleocharis atropurpurea (Retz.) J. Presl & C. Presl

Pl. 75 e, f; Map 275

Plants annual, tufted. Aerial stems 3–15 cm long, 0.2–0.3 mm in diameter, more or less circular in cross-section and finely ridged, lacking cross-lines. Basal sheaths tinged reddish purple to dark brown toward the base, the tip firm or somewhat membranous, oblique, and tapered to a point on 1 side. Spikelets 2–8 mm long, oblong to ovate in outline, pointed or rounded at the tip, with 1 sterile, basal scale. Scales 1.0–1.5 mm long, ovate, rounded at the tip, with a broad, green or straw-colored central area and dark brown to purplish black margins. Perianth bristles lacking or 1–5, shorter than the fruit, often becoming detached during fruit development, usually finely retrorsely barbed. Stigmas 2. Fruits 0.5–0.6 mm long, the main body obovate in outline, biconvex and flattened in cross-section, the surface smooth, dark reddish black to black, shiny. Tubercles tiny, flattened-triangular. 2n=20. June–August.

Known from a single collection from the Missouri River floodplain in Platte County (U.S., southwestern Canada, Mexico, Central and South America, Caribbean Islands, Europe, Asia, Africa). Mudflats near edge of marsh.

This pantropical species was first discovered in Platte County in 1982 (Castaner, 1984). It should be searched for elsewhere in the Missouri River floodplain.