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Cyperus
See list of 22 species in this genusReference: Tucker et al. (2002).
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1a. Styles bifid; achenes lenticular to biconvex in cross-section; edge of achene facing and fitting into a groove in rachilla
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2a. Achenes broad-obovate to nearly suborbicular in outline, minutely marked with elongate, superficial cells and irregular, pale transverse lines at maturity; floral scales broad-ovate; flowers with usually 3 stamens
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2b. Achenes ovate to oblong, obovate, or narrow-obovate in outline, unmarked; floral scales narrow-oblong to ovate; flowers with 2 stamens (upper flowers sometimes with 3 stamens)
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3a. Floral scales pigmented, in part, with anthocyanins (i.e., red-brown to purple-brown), rarely pale throughout, without a projecting mucro at the apex; achenes ovate to obovate in outline, rounded to broad-acute at apex, compressed to biconvex in cross-section
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4a. Style divided nearly to its base, usually persistent in fruit; anthocyanic pigments most prominent along medial and apical margin of floral scales and along upper edges of midribs, with a conspicuous pale area between the midrib and margin [Fig. 105]
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4b. Style connate in the basal ⅓, often deciduous from the fruits; anthocyanic pigments most prominent in basal and medial portion of floral scales, fading toward apex, the pigmented region not outlining a conspicuous pale region on each side of the scale [Fig. 104]
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3b. Floral scales lacking anthocyanic pigments, stramineous, gold-brown, to brown (sometimes light chestnut-brown), with a short mucro at the apex; achenes oblong in outline, truncate to obtuse at apex, biconvex (sometimes widely so) in cross-section
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5a. Achenes narrow-obovate in outline; floral scales 2.5–3.5 mm long
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5b. Achenes oblong in outline; floral scales 1.5–2.3 mm long
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1b. Styles trifid; achenes triangular in cross-section; one surface of achene facing and resting flat on rachilla
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6a. Plants annual, with soft stem-bases from a fibrous root-system, lacking rhizomes and knotty tubers
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7a. Floral scales with 2 keels in the basal 30–60%; flowers with 1 stamen
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7b. Floral scales either with a single keel or merely nerved and lacking keels altogether; flowers with 2 or 3 stamens (only 1 stamen in C. squarrosus)
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8a. Floral scales squarrose at apex [Fig. 109]; flowers with 1 stamen; dwarf plants 5–20 cm tall, when fresh with a sweet scent suggesting Melilotus or Ulmus rubra
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8b. Floral scales not outcurved at tip [Fig. 110]; flowers with 2 or 3 stamens; plants predominantly taller, 10–80 cm in height, without a sweet scent
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9a. Floral scales 7- to 13-nerved, (1.5–) 2–4.5 (–5) mm long
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10a. Floral scales (3–) 3.2–4.5 (–5) mm long; spikelets disarticulating from the base and falling intact; achenes broad-linear to narrow-oblong in outline; stems usually arising from a swollen, corm-like base (in part)
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10b. Floral scales (1.5–) 2–2.8 (–3.2) mm long; spikelets disarticulating into segments at maturity, each segment consisting of a floral scale and a winged rachilla joint; achenes elliptic to narrow-obovate in outline; stems not arising from a corm-like base
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9b. Floral scales 3- to 5-nerved, 0.5–1.7 mm long
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11a. Floral scales broad-obovate to suborbicular; achenes 1–1.5 mm long, brown to nearly black at maturity
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12a. Spikes ascending to appressed; distance between floral scales on same side of rachis 0.7–0.9 mm; floral scales tipped by a mucro 0.05–0.12 mm long
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12b. Spikes spreading; distance between floral scales on same side of rachis 1.1–1.5 mm; floral scales tipped by a mucro 0.2–0.25 mm long
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11b. Floral scales ovate; achenes 0.7–1 mm long, pale gray-brown to nearly white at maturity
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13a. Spikelets radiating from the summit of short axes, forming subcapitate clusters; rachilla lacking a prominent wing-margin; roots brown
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13b. Spikelets serially disposed along elongate axes, forming cylindric clusters; rachilla wing-margined; roots anthocyanic
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6b. Plants perennial, with firm stem-bases arising from rhizomes, knotty tubers, or a swollen corm-like base [Fig. 106]
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14a. Spikelets with 3–5 floral scales, crowded into dense, cylindrical to subglobose clusters, mainly only the tips of the spikelets visible in life
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15a. Spikelets (3.5–) 4–7 mm long, with membranaceous, yellow-brown to brown floral scales 3.5–4.5 mm long; spikes globose to short-ovoid; achenes 1.5–2.3 mm long; bracts scabridulous along adaxial surface (especially distally); stems growing singly or loosely cespitose
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15b. Spikelets 2.2–4 (–4.5) mm long, with coriaceous, brown to yellow-brown or red-brown floral scales 1.8–2.5 mm long; spikes obloid-ovoid; achenes 1.2–1.7 mm long; bracts smooth along adaxial surface, scabridulous only along margins; stems densely cespitose
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14b. Spikelets with 3–20 (–50) floral scales, loosely to moderately crowded, many spikelets visible throughout their length [Fig. 110]
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16a. Floral scales with 2 keels in the basal 30–60%; flowers with 1 stamen
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16b. Floral scales either with a single keel or merely nerved and lacking keels altogether; flowers with 3 stamens
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17a. Spikelets flat, serially disposed on elongate axes, forming cylindric clusters [Fig. 110]
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18a. Floral scales (3–) 3.5–4.5 (–5) mm long, keeled along their midrib, persistent and falling with the rachis; plants lacking well-developed rhizomes, the stems emerging from a tuberous base; achenes broad-linear to narrow-oblong in outline (in part)
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18b. Floral scales 2.3–3 mm long, not or scarcely keeled, deciduous from the rachis; plants with long, slender rhizomes ending in tubers; achenes oblong to narrow-obovate in outline
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17b. Spikelets compressed to subterete, radiating from the summit of short axes, forming hemispherical to subglobose clusters [Figs. 107,108]
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19a. Floral scales with 3–5 nerves arranged close to the center of the scale (i.e., the sides largely nerveless); achenes up to 1 mm long; spikelets often proliferated into vegetative propagules
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19b. Floral scales with 7–13 nerves, these more widely distributed and only the very margin nerveless; achenes 1.4–3 (–3.5) mm long; spikelets not proliferous
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20a. Floral scales suborbicular; achenes with 1 or more evidently concave faces, up to 1.5 times as long as wide
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20b. Floral scales broad-elliptic to oblong or ovate; achenes with flat or slightly concave faces, 2 or more times as long as wide
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21a. Stems often scabrous near apex; floral scales with a short awn 0.5–1 mm long; achenes 2–3 (–3.5) mm long; spikelets ascending [Fig. 108]
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21b. Stems smooth; floral scales blunt or with a minute mucro up to 0.2 mm long; achenes 1.4–2.2 mm long; basal spikelets of cluster horizontally spreading to reflexed [Fig. 107]
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22a. Involucral bracts ascending to sometimes spreading-ascending, with smooth to obscurely scabrous margins, numbering 3–7 per cluster; rachilla broadly wing-margined; inflorescence with (2–) 4–10 elongate rays; anthers 0.7–1 mm long
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22b. Involucral bracts mostly spreading to reflexed, with scabrous margins, numbering 2–4 per cluster; rachilla sharp-edged to narrowly winged; inflorescence with a solitary, sessile cluster or also with 1–4 rays [Fig. 107]; anthers 0.3–0.6 mm long
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Each photo represents one species in this genus.