Herbs, perennial, rhizomatous. Culms solitary or close together, trigonous, 5-40(-95) cm, glabrous. Leaves (2-)3-7, broadly V-shaped, 3-20(-30) cm × 1.5-3 mm. Inflorescences: spikes loosely to densely ovoid to hemispheric, 7-16 mm diam.; rachis 1-2 mm, or absent; rays 1-2, 3-45 mm; if rays absent, inflorescence sessile, dense, 6-20 mm diam; bracts 2-3, horizontal to reflexed downward, broadly V-shaped, 1-15 cm × 1-3 mm. Spikelets (3-)5-25(-60), linear to oblong-linear, (3-)5-9 × 1.8-2.3 mm; floral scales 4-18, closely imbricate, chestnut brown, black, or brown, medially green or greenish brown, laterally ribless, medially 2(-3)-ribbed, distinctly 2-keeled basally, ovate to orbiculate, 1.5-2.1 × 1.4-2.2 mm, apex obtuse. Flowers: stamens 2; anthers 0.6-0.8 mm, connectives not prolonged; styles 0.4-0.6 mm; stigmas 0.7-2.1 mm. Achenes brown, ellipsoid, 1.2-1.4 × 0.6-0.8 mm, network of ridges forming isodiametric or square cells, slightly stipitate, apex apiculate, surfaces minutely punctate.
Fruiting summer. Swamps, ditches, wet pastures, seeps in montane forests; 0-1200 m; Ariz., Calif., N.Mex., Okla., Tex.; Mexico; Central America; South America.
Six varieties (Cyperus niger var. niger, var. castaneus, var. robustus, var. lorentizianus, var. intricate-ramosus, and var. pseudo-elegantulus) were recognized by G. Kükenthal (1935-1936). Based on field observations and measurements of hundreds of collections from Mexico, where the species is most plentiful, it does not seem possible to recognize any of the infraspecific taxa (G. C. Tucker 1983, 1994; G. C. Tucker and R. McVaugh 1993).
Tucker 1994, FNA 2002
Common Name: black flatsedge Duration: Perennial Nativity: Native Lifeform: Graminoid General: Rhizomatous perennial with rhizomes about 1 mm in diameter, stems soft and spread 1-30 mm apart, 5-40 cm tall, less than 1.5 mm in diameter, three sided to three edged and smooth. Vegetative: Leaves 3-7, 3-20 cm long, 1.5-3 mm wide, broadly v-shaped, margins rough to the touch. Inflorescence: Subtending bracts 2-3, 1-15 cm long, 1-3 mm wide, broadly v-shaped, margins and keel rough to the touch, horizontal to reflexed downward parallel to the stem, inflorescence 6-20 mm in diameter, densely ovoid, rays 1-2, 3-45 mm,spikes 7-16 mm in diameter, loosely to densely ovoid to hemispherical spikelets 5-25, 5-9 mm long, 2-3 mm wide, linear to oblong-linear, flattened, 4-18 deciduous scales, 1.5-2 mm long, 1.5-2 mm wide, ovate to orbiculate, obtuse apex, black; achenes 1-1.5 mm long, lenticular, ovoid-ellipsoid, apiculate apex, faces convex with equal diameter cells forming transverse undulations. Ecology: Found in wet meadows, seeps, springs, and stream banks from 3,500-7,000 ft (1067-2134 m); flowers July-October. Notes: Distinguished by the blackish spikelets and lenticular achenes. The roots, while rhizomatous, are very fibrous. Ethnobotany: Unknown Etymology: Cyperus is from the Greek word meaning sedge, while niger means black. Synonyms: Cyperus diandrus var. capitatus, Cyperus melanostachyus, Cyperus niger var. capitatus, Cyperus niger var. castaneus, Pycreus niger Editor: SBuckley, 2010