44. Cyperus esculentus Linnaeus, Sp. Pl. 1: 45. 1753.
Herbs, perennial, stoloniferous; stolons soft, spongy, flexible when dried, 2–8(–15) cm, bearing tubers (3–)6–11 mm diam. Culms trigonous, 15–60 (–100) cm × 0.6–3.4 mm, glabrous. Leaves 3–7, flat to V-shaped or flanged V-shaped, (6–)20–40(–80) cm × 2–4 (–6.5) mm. Inflorescences: spikes broadly ellipsoid to ovoid or hemispheric, (12–)18–30 × (12–)18–35 mm; rachis 4–17 mm; rays 4–10, (0.3–)2–12 cm; bracts (3–)4–5(–7), ± horizontal to ascending at 45(–75)°, V-shaped to flanged V-shaped, (1.5–)5–30 cm × 0.5–4 mm; rachilla persistent, wings hyaline, 0.3–0.5 mm wide. Spikelets (3–)10–20(–28), divaricate or ascending, yellowish brown to dark brown, linear to linear-lanceoloid, compressed-quadrangular, (5–)10–20(–55) × (1.2–)1.4–2(–3) mm; floral scales persistent, 6–34, spreading or appressed, ovate-lanceolate, laterally 7–9-ribbed, laterally yellowish brown to dark brown medially brownish, reddish, or greenish, ovate, or ovate-deltate, medially 3-ribbed, 1.8–2.7(–3.4) × (1–)1.5–1.8(–2.4) mm, apex acute or sub-acute. Flowers: anthers (1–)1.2–1.5(–2.1) mm; styles (0.7–)1–1.2(–2.2) mm; stigmas (1.2–)1.8–2.3(–4) mm. Achenes (seldom maturing) brown, sessile, ellipsoid, (1.1–)1.3–1.5(–1.6) × 0.3–0.6(–0.8) mm, apex obtuse, surfaces puncticulate.
Varieties 4 (3 in the flora): nearly worldwide.
Cyperus esculentus is a widespread and polymorphic species. Although seven varieties have been recognized (G. Kükenthal (1935–1936), recent studies based primarily on spikelet features provided support for four varieties (P. Schippers et al. 1995). Cyperus esculentus var. esculentus is restricted to the Old World.
SELECTED REFERENCE
Schippers, P., S. J. TerBorg, and J. J. Bos. 1995. A revision of the infraspecific taxonomy of Cyperus esculentus (yellow nutsedge) with an experimentally evaluated character set. Syst. Bot. 20: 461–481.
