2. Cyperus bipartitus Torr. (nutgrass)

Pl. 69 j, k; Map 246

C. rivularis Kunth

C. rivularis f. elutus (C.B. Clarke) Kük.

Pycreus bipartitus (Torr.) C.B. Clarke

Plants annual, tufted, lacking rhizomes and tubers. Aerial stems 3–35 cm long, erect to spreading, bluntly trigonous, smooth. Leaf blades 1–18 cm long, 1–3 mm wide (sometimes folded longitudinally and thus appearing narrower), shorter than the stems. Inflorescences of 1–5 sessile spikes or irregular umbels with 1–3 sessile spikes and 1–5 rays, each ray smooth, ending in a cluster of 1 to few sessile spikes. Inflorescence bracts 2–3, mostly much longer than the rays, ascending. Spikes 7–20 mm long, with 3–10 spikelets, broadly ovoid, headlike, open, usually somewhat flattened, the spikelets spreading to ascending, attached near the tip of the axis, the spikelet bases usually visible. Spikelets 8–18 mm long, 2.0–3.5 mm wide, oblong to narrowly elliptic, usually pointed at the tip, strongly flattened in cross-section, with 6–30 florets, the fruits and scales shed successively from the base to the tip, leaving the persistent axis. Spikelet axis not winged. Spikelet scales 2.0–2.5 mm long, strongly overlapping, appressed to ascending, oblong-ovate, bluntly to fairly sharply angled along the back, rounded to bluntly pointed and slightly incurved at the tip, with 1–3 nerves, reddish brown (or rarely entirely straw-colored to light green), the reddish purple pigmentation best developed near the base, often tapered to a band near each margin toward the tip, the midrib usually green. Stamens 2(–3), the anthers 0.4–0.5 mm long. Stigmas 2, the styles (including stigmas) divided less than 2/3 of the way to the base, often only slightly extended past the subtending scale. Fruits 1.0–1.5 mm long, ovate to obovate in outline, biconvex and somewhat flattened in cross-section, the surface with a very fine pattern of 4–5-sided cells that are about as long as wide (visible under magnification), greenish brown to dark brown or nearly black at maturity, less commonly coated with a gray layer, shiny, sometimes somewhat iridescent. 2n=54. July–October.

Scattered nearly throughout Missouri (eastern U.S. and adjacent Canada west to North Dakota and Texas; also Washington to California; Mexico south to South America). Margins of streams, spring branches, ponds, and lakes, fens, and moist depressions of glades; also sandy to gravelly roadsides and moist, open areas.

In Missouri, C. bipartitus often occurs in mixed populations with the morphologically very similar C. flavescens.