Cyperus reflexus
Cyperus rotundus
bentawn flatsedge
chaguan humatag, coco-grass, nutgrass, pakopako, purple nut-sedge
roundly trigonous to terete, 30–80 cm × 1–1.6 mm, glabrous.
trigonous, 10–35(–40) cm × 0.7–3.4 mm, basally indurate, glabrous.
1–6, 10–40 cm, glabrous or essentially so.
V-shaped to flanged V-shaped, 5–30 cm × 2–6 mm.
heads ovoid to pyramidal, 9–15 mm diam.;
rays 0 or 3–6, 0.5–4 cm, glabrous;
bracts 3–4, longest erect, appearing as continuation of culm, others horizontal to ascending, 4–17 cm × 1.5–4 mm.
spikes 1(–3), broadly ellipsoid, (12–)15–25(–30) × (12–)20–30(–50) mm, rays (3–)4–6(–7), 0.2–10 cm;, bracts (2–)3–5, horizontal to ascending at 45°, V-shaped to flanged V-shaped, 0.5–10 cm × 0.5–4 mm, rachilla persistent, wings 0.5–1 mm wide.
25–60, reddish with contrasting yellowish or greenish edges, oblong-lanceoloid, strongly compressed, 5–6(–15) × 1.5–2.5 mm;
floral scales 10–22, laterally reddish, medially yellowish green, 2-keeled, laterally strongly 1-ribbed on each side, proximally grooved, ovate-elliptic, 1.4–2.2 × 0.8–1.5 mm, apex acute, apically scabridulous (sometimes glabrous).
(2–)3–7(–12), compressed, linear, 4–40 × 1.3–1.8 mm, floral scales persistent, 6–36(–42), spreading or appressed, purple to reddish brown, with narrow clear border and green midrib, 7–9-ribbed, ovate, (1.8–)2.6–3.4 × 2.2–3 mm, apex obtuse.
stamen 1;
anthers 0.6–1 mm;
styles 0.3–0.5 mm;
stigmas 0.3–0.6 mm.
anthers 1–2.5 mm, styles 1.3–3.5 mm, stigmas (1.8–)2–3.3 mm.
reddish brown, stipitate, ovoid-ellipsoid, 0.8–0.9 × 0.3–0.4 mm, stipe 0.1–0.2 mm, apex acute to acuminate, surfaces reticulate or subtly rugulose.
black, sessile, ellipsoid, abaxial face convex, adaxial face concave, 1.4–1.7(–1.9) × 0.8–1 mm, apex obtuse, surfaces puncticulate.
Cyperus reflexus
Cyperus rotundus
Cyperus reflexus is recognized by its reddish scales with contrasting greenish or yellow keels and by the laterally 1ribbed scales. The lateral rib is most often situated where the reddish and yellowish parts of the scale meet. Two varieties of C. reflexus, var. reflexus and var. fraternus, have been recognized (M. F. Denton 1978b). Both varieties were noted as intermingled in the North American and South American segments of the widely disjunct range of C. reflexus. Such variation does not seem significant at the varietal level (see G. C. Tucker 1994; G. C. Tucker and R. McVaugh 1993).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Cyperus rotundus is documented in Connecticut, Delaware, New York, and Pennsylvania; there is no evidence of persistent populations.
Cyperus esculentus and C. rotundus are the only two species of subg. Cyperus in the New World that produce tuberiferous stolons. The two species also have persistent floral scales and persistent rachillas, a combination of characteristics not found in any other New World species of Cyperus.
Cyperus rotundus is distinguished from other species of the genus in the New World by its open spikes composed of linear reddish spikelets borne on a conspicuous slender rachis. Cyperus rotundus is usually acknowledged to be the world’s worst weed (cf. G. C. Tucker 1987). In the United States, it does not grow north of the mean 1°C January isotherm. Cyperus esculentus (preceding species) is a serious weed in much of the world, especially in cooler regions where the more tropical C. rotundus does not grow. Cyperus esculentus is able to tolerate lower air temperatures (as low as -18°C). The two species apparently differ also in their thermal optima for growth.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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