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Key to Cyperus

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1 Floral scales spirally imbricate.
..2 Leaves many, cauline, coriaceous, closely spaced distally; culms arising from long, thick, branched rhizomes; inflorescence dense, capitate; [FL, beaches and coastal dunes]; [section Remirea]
..2 Leaves basally disposed; inflorescence of 1-5 sessile ovoid spikes, or more diffuse.
....3 Spikelets many, in densely globose to pyramidal heads, these borne on elongate rays or sessile; rhizomatous perennials, forming extensive floating mats; [section Oxycaryum]
....3 Spikes [actually consisting of numerous highly reduced, spirally imbricate spikelets each with 1-2 (-3) scales] 1-5, terminal and capitate on the culm; terrestrial, often diminutive annuals; [subgenus Lipocarpha].
1 Floral scales 2-ranked and distichously imbricate.
......4 Spikelets reduced, 1(-2)-flowered with 2-3 scales, flattened, ovoid or lanceoloid, mostly < 5 mm long; rays absent, spikes 1-4, very dense, ovoid to oblong; stigmas 2; achenes biconvex; [subgenus Kyllinga].
......4 Spikelets 1-many-flowered (if all only 1-3-flowered then subterete to quadrangular in cross-section and ellipsoid to linear); rays present or absent, inflorescence mostly not as above.
........5 Stigmas 2; achenes laterally flattened, lenticular (to compressed-subterete), borne with an edge to the rachilla, spikelets thus laterally flattened.
..........6 Achene emarginate or obcordate at apex; rachilla deciduous, basally articulate; spikelets ovate-lanceolate, with 4-6(-8) fertile scales, these shortly but distinctly mucronate [introduction, FL]; [subgenus Queenslandiella]
..........6 Achene obtuse to truncate at the apex, sometimes apiculate; rachilla persistent; spikelets (at least the larger) lanceolate to linear, usually with 8 or more fertile scales, obtuse to acute, or (C. pumilus) excurved-cuspidate; [subgenus Pycreus]
........5 Stigmas 3 (2 in subg. Juncellus species, sometimes 2 and 3 in C. alopecuroides); achenes either trigonous or dorsiventrally compressed and borne with a face to the rachilla; spikelets terete or quadrangular to strongly compressed-quadrangular or compressed-subterete.
............ 7 Rachilla corky-thickened, transversely articulated at the base of each scale, the spikelets at maturity separating into 1-fruited dispersal units, each with 1 scale, the rachilla segment and wings, conspicuously clasping the achene (spikelets visibly “jointed”, at maturity breaking apart); spikelets linear, terete or scale tips slightly spreading.
............ ..8 Spikelets 2-8, rays absent (the spikelets in a single digitate cluster at the top of the culm, appearing lateral); bracts 2-3, longest erect, filiform, ≤ 1 mm wide [pine rocklands, s. peninsular FL]; [section Filiformes, apparently allied with C. fuligineus]
............ ..8 Spikelets 10-60, rays usually present and well-developed; bracts 4-10, spreading to ascending, mostly leafy, ≥1mm wide. [widespread, often weedy]; [section Diclidium]
............ ....9 Tip of each scale not reaching above the base of the next distal scale on the same side of the rachilla, and usually ending short of it; achene linear-oblong, 1.5-2 mm long, ca. 3× as long as wide.
............ ....9 Tip of each scale surpassing the base of the next distal scale on the same side of the rachilla; achene ellipsoid or obovoid-oblong, 1-1.5 mm long, ca. 2× as long as wide
............ 7 Rachilla not transversely articulated; scales persistent or deciduous; rachilla wings present or absent, not corky, clasping the achene or not; spikelets ovoid to linear, compressed, quadrangular, or terete.
............ ......10 Spikelets in dense glomerulate heads or digitate clusters, the rachis essentially absent; spikelets strongly laterally compressed; [subgenus Pycnostachys].
............ ......10 Spikelets in spikes (sometimes sessile and capitate), arranged along a well-developed rachis, this sometimes obscured but evident upon dissection; spikelets quadrangular or terete to moderately compressed.
............ ........11 Longest bract vertical, appearing as a continuation of the culm; rays absent, spikelets 2-7(-14), in a single digitate cluster; achenes dorsiventrally compressed, with the achene face toward the rachilla, the spikelets subterete (elliptic in cross-section) [rare waif, brackish marshes]; [subgenus Juncellus, section Laevigati]
............ ........11 Longest bract not appearing as a continuation of the culm; rays present or absent; inflorescence not as above (sometimes sessile and capitate, but then with 15 or more spikelets); achenes trigonous or dorsiventrally compressed; [subgenus Cyperus].

Key to Cyperus, Key A: Key to subgenus Lipocarpha

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1 Inflorescence terminal, the bracts 2-3, deflexed to ascending; spikes (1-) 2-5, each 2-10 (-12) mm long; achenes narrowly obovoid, 3.3-5× as long as wide; anthers ca. 0.25 mm long, or longer; [section Lipocarpha]
..2 Scale apex (the outer 0.2-0.3 mm) excurved, acuminate; stigmas 2; anthers ca. 0.25 mm long
..2 Scale apex straight to incurved; stigmas 3; anthers ca. 0.5 mm long
1 Inflorescence appearing lateral, the bracts 1-2 (-3), the longest held vertical and appearing as a continuation of the culm; spikes 1-2 (-3), each 1-5 (-8) mm long; achenes obovoid or ellipsoid, 1.5-2.5× as long as wide; anthers 0.1-0.2 mm long.
....3 Stigmas 3; outer scales ca. 2 mm long, the greenish midrib projecting as a long, excurved cusp; plants relatively robust, culms 5-30 cm tall, ca. 0.7 mm thick; [rare waif, FL]; [section Rikliella]
....3 Stigmas 2; outer scales 0.5-1.6 mm long, acute to acuminate, incurved to slightly excurved; plants diminutive, culms 2-15 (-20) mm tall, 0.3-0.5 mm thick; [collectively widespread]; [section Neohemicarpha]
......4 Outer scale 0.5-1 mm long; inner scale bifid, to 0.2 mm long or absent; [widespread in our region]
......4 Outer scale 0.9-1.6 mm long; inner scale oblong, 0.5-0.8 long; [IL and LA westwards].
........5 Outer scale widest about at mid-length, acuminate, excurved; inner scale usually veinless (rarely with 2-4 reddish veins)
........5 Outer scale widest above mid-length, mostly acute, incurved; inner scale with 2-4 reddish veins

Key to Cyperus, Key B: Key to subgenus Kyllinga

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1 Scale keel conspicuously winged, laciniate; anthers 2 mm long; achenes ca. 1.2 mm wide, ovate to nearly orbicular; fibrous-rooted annual; [section Kyllinga]
1 Scale keel toothed or entire; anthers <2 mm long; achenes 0.5-1 mm wide, elliptic to obovate or oblong; perennials (except C. hortensis); [section Brevifoliae].
..2 Plants with culms arising singly along a scaly, creeping rhizome; spikes green.
....3 Central spike 8-10 mm wide, globose, solitary; inflorescence bracts deflexed to spreading (divaricate); style 0.6-1.2 mm long; anthers 2-3; scale keel entire
....3 Central spike 3-7 mm wide, ovoid to oblong, often branched; longest inflorescence bract held vertical on most culms; style 1.8-2.2 mm long; anther 1; scale keel denticulate
..2 Plants cespitose or with very slender, easily broken stolons and cormose culm bases; spikes white (except C. hortensis).
......4 Spikes green; plants cespitose, fibrous-rooted annuals; scale keels denticulate; achene light brown, oblong, 2× as long as wide
......4 Spikes whitish; plants cespitose or stoloniferous perennials; scale keels entire; achenes various.
........5 Mature achene light brown, oblong to obovate; plants reproducing by very slender, easily broken stolons; spikes ovoid to pyramidal.
........5 Mature achene black, with whitish (pale) stipe and apiculus, broadly elliptic; plants cespitose; larger (central) spikes oblong to cylindric.

Key to Cyperus, Key C: Key to subgenus Pycreus – stigmas 2; achenes lenticular;
achenes laterally flattened, borne with an edge toward the rachilla

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1 Scales awned or cuspidate, cusp 0.3-0.5 mm long, excurved; achenes 0.6 mm long; [section Pumili]
1 Scales obtuse to slightly mucronate, apex not notably excurved; achenes (0.7-)1-1.6 mm long.
..2 Floral scales divaricate (thus the spikelet margin appearing coarsely dentate), with whitish or hyaline margins; coarse, erect plants 30-75cm tall, inflorescence diffuse; [section Albomarginati]
..2 Floral scales with tips appressed (proximal sometimes spreading in C. polystachyos), lacking hyaline border; plants mostly smaller.
....3 Achenes oblong, subterete, often only slightly compressed, apex truncate, apiculate; scales 3-5-nerved; spikelets mostly <2 mm wide (except C. filicinus); [section Pycreus].
......4 Scales 2.5-3.6 mm long, 1.6-1.8 mm wide; achenes 1.2-1.6 mm long, 0.6-0.9 mm wide, narrowly obovoid; [beaches, maritime habitats]
......4 Scales 1.3-2.4 mm long, 1.0-1.4 mm wide; achenes 0.8-1.2 mm long, 0.4-0.6 mm wide; [habitats various]
........5 Cespitose annual, < 12 cm tall; floral scales ovate, 1.3-1.6 mm long, loosely imbricate; styles 0.1-0.2 mm long; stigmas 0.3-0.4 mm long; filaments 1.2-1.4 mm long; anthers 0.1-0.2 mm long; achenes stipitate, strongly compressed laterally; [LA and westwards, rare]
........5 Shortly rhizomatous perennial, mostly > 12 cm tall; floral scales oblong, 1.8-2.4 mm long, closely imbricate; styles 0.6-1 mm; stigmas 1.4-2 mm long; anthers 0.6-0.8 mm long; achenes substipitate to cuneate, slightly compressed laterally; [widespread]
....3 Achenes ovoid, ellipsoid, or obovoid, biconvex, apex rounded to acute; scales bicarinate medially; spikelets mostly > 2mm wide.
..........6 Achenes black to dark reddish brown, with encrusted transverse whitish lines, epidermal cells longitudinally elongate, rectangular; scales pale brown or yellowish, the dark achenes strongly contrasting and visible through the spikelets in life (without backlighting); fibrous-rooted annuals; [section Zonati].
..........6 Achenes black to brownish, without transverse lines, epidermal cells square or isodiametric; plants either perennials or scales darker.
............ 7 Scales uniformly pale yellowish to yellowish brown; cespitose perennials, rhizomes short; [section Propinqui].
............ ..8 Anthers ellipsoid, 0.3-0.6 mm long; spikelets 1.8-3 mm wide, with scales 1.8-2.6 mm long; achenes brown, ellipsoid, ovoid, or obovoid, 0.4-0.8 mm wide; [more widespread]
............ ..8 Anthers linear, 2-2.4 mm long; spikelets 3-5 mm wide, with scales (3.6-) 3.8-4.2 (-4.6) mm long; achenes black, broadly obovoid to orbiculate, 0.8-1 mm wide; [s. peninsular FL, rare waif]
............ 7 Scales with anthocyanic (reddish-brown or purplish) pigmentation; fibrous-rooted annuals (except C. sanguinolentus); [section Vestiti].
............ ....9 Floral scales firmer, subcoriaceous, not bilaterally sulcate; reddish pigmentation ±uniformly distributed or concentrated basally and medially; floral scales 2.5-3 mm long; annuals, culms usually <25 (35) cm long
............ ....9 Floral scales membranous, each side with a narrowly elliptic, shallow, pale, translucent groove outlined at least marginally by reddish pigmentation; floral scales 1.8-2.7 mm long; annuals or perennials.
............ ......10 Cespitose annuals, culms usually < 25 (-35) cm tall; stamens 2; style divided nearly to base; style branches conspicuously exserted beyond floral scale, exposed portions about as long as floral scale
............ ......10 Rhizomatous perennials, culms usually > 25 cm tall; stamens 3; style divided less than half its length; style branches not so conspicuously exserted, exposted portions less than half as long as floral scale

Key to Cyperus, Key D: Key to subgenus Pycnostachys -- stigmas 3; achenes trigonous; rachis essentially absent,
spikelets borne in digitate clusters or in umbellate or glomerulate heads

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1 Scales cuspidate, with an excurved, awnlike tip (0.3-) 0.5-1 (-1.3) mm long
1 Scales rounded to minutely mucronate (mucro <0.3mm), incurved to excurved.
..2 Leaves mostly reduced to bladeless sheaths; inflorescence bracts 18-22 subequal, large and conspicuous; [the “umbrella sedge” common in the nursery trade]; [section Alternifolii]
..2 Leaf blades present (absent in C. haspan and C. prolifer); inflorescence bracts 2-10 (rarely more, then markedly unequal).
....3 Scales with 1 central nerve on back, 2-keeled in lower 30-60%, nerves absent elsewhere or scales with 1 lateral rib on each side; spikelets with scales closely overlapping, aggregated into numerous dense glomerulate heads borne on elongate rays; [section Luzuloidei]
....3 Scales conduplicate their entire length, or broadly rounded on back, not 2-keeled as above, 5-11 nerved, medially 3-nerved, or occasionally with 2 indistinct lateral ribs and a single main keel nerve; spikelets in loose digitate clusters, or inflorescence congested into a single capitate cluster; [sections Fusci, Haspani, and Diffusi]

Key to Cyperus, Key E: Key to subgenus Cyperus – stigmas 3; achenes trigonous; spikelets borne in spikes on a well-developed rachis;
rachilla continuous, or articulate only at the base

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1 Leaf blades absent; culms 15-50 mm thick, nearly terete; inflorescence open and diffuse, primary rays 10-30 cm long, bearing numerous 2nd and 3rd order rays up to 20 cm long and bracts to 25 cm long, often drooping; anther connectives subulate, projected beyond the anther 0.2-0.5 mm; [exotics, commonly cultivated, rarely naturalizing]; [subgenus Cyperus, section Papyrus]
..2 Rays stiff, ascending to erect; primary bracts (8-) 20-45 cm long
..2 Rays slender, drooping or arching; primary bracts 3-8 cm long
1 Leaf blades well-developed (except C. articulatus); culms < 20mm thick, trigonous if broader than 5 mm; inflorescence smaller, more congested (except C. prolixus); anther connectives not prolonged.
....3 Spikelets quadrangular to subterete, 1-1.5× as wide as thick; floral scales 1-8, persistent and tightly appressed (rarely slightly ascending); rachilla articulate at the base, the whole spikelet falling as a unit at maturity
....3 Spikelets compressed-quadrangular or compressed-subterete, mostly 2× or more as wide as thick (less compressed in C. erythrorhizos and some forms of C. esculentus and C. rotundus); scales 1-many, deciduous or persistent; rachilla persistent or deciduous after the scales.
......4 Spikes long-cylindric, with (25-) 35-80+ spikelets, and well-developed branches or 2nd order rays; scales deciduous, minute, (1.1-) 1.3-1.8 mm long, (6-) 12-20 (-30) per spikelet; spikelets quadrangular, slightly compressed (subterete in C. alopecuroides); achenes (0.4) 0.7-1 (-1.2) mm long, often moderately dorsiventrally compressed or plano-convex; plants coarse perennials, culms 5-25 dm tall, 5-50 mm in diameter (C. erythrorhizos keyed under both leads).
........5 Stigmas 2, or 2 and 3 on a plant; spikes narrowly cylindric, the rachis obscured by the densely packed, ascending, imbricate spikelets; spikelets subterete, somewhat compressed, ovoid to oblong; rachilla wings absent to 0.1 mm wide; achene lenticular, its face against the rachilla [rare waif, FL]; [section Alopecuroides]
........5 Stigmas 3; spikes less dense, spikelets spreading to divaricate; spikelets quadrangular, linear; rachilla winged, wings 0.3 mm wide; achenes not as above [collectively widespread]; [section Fastigiati].
..........6 Plants perennial, with indurate rhizomes (sometimes inconspicuous); roots not reddish; floral scales 1.6-1.8 mm long; anthers 0.4-0.5 mm long; culms robust, trigonous, 5-25 dm tall, 5-15 mm wide
..........6 Plants annual; roots reddish, fibrous; floral scales 1.3-1.5 mm long; anthers 0.2-0.3 mm long; culms shorter, mostly rounded, (0.05-) 0.5-2.5 (-10.5) dm tall, 1-7.5 mm wide
......4 Spikes not as above; scales persistent or deciduous, mostly > 1.8 mm long (except sections Iriodei and Aristati); achenes > 1 mm long, trigonous (dorsiventrally compressed in C. nipponicus and C. serotinus); culms mostly < 10 dm tall, < 7.5 mm in diameter (except C. prolixus).
............ 7 Spikelets 1.2-1.5 (-1.6)mm wide, only compressed proximally, filiform distally; adjacent scales spaced apart on the same side of the rachilla; rachilla wings absent or very reduced; [subgenus Cyperus, section Distantes]
............ 7 Spikelets mostly broader, not filiform distally; scales apices reaching or exceeding the base of the next scale on the same side of the rachilla; rachilla wings present or absent.
............ ..8 Scales strongly 5-nerved, obovate-orbiculate, 1-1.5 mm long, divaricate, scarcely overlapping, apex emarginate and mucronulate; style < 0.1 mm long; inflorescence diffuse, secondary rays present, spikelets widely spaced on elongate rachises; [weedy exotics]; [section Iriodei]
............ ....9 Mucro ≤ 0.12 mm long; spikelets appressed to erect-ascending
............ ....9 Mucro 0.2-0.3 mm long; spikelets divaricate
............ ..8 Scales variously nerved, but at least 1.8 mm long (if shorter, with an excurved cusp > 0.5 mm long), not emarginate; style at least 0.5 mm long; inflorescence generally more congested.
............ ......10 Scales cuspidate to awned, midrib excurrent at least 0.3 mm, conspicuously excurved (straight in C. compressus and C. nipponicus); plants either diminutive fibrous-rooted annuals, culms often decumbent, or cespitose perennials (section Elegantes) with involute leaves and vegetative parts viscid (sticky).
............ ......10 Scales acute, midrib not notably projecting, apices not excurved; plants erect, rhizomatous, stoloniferous, cormose-based, or cespitose perennials, vegetative parts not viscid, leaves plane or V-shaped (cuspidate perennial species also keyed above).
............ ........11 Stigmas 2; achenes dorsiventrally compressed; spikelets subterete, elliptic in ×-section; [subgenus Juncellus, section Stoloniferi]

Key ZA: Key to Cyperus of various affinities -- Scales cuspidate to awned

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1 Leaves, bracts, and culms viscid (sticky); leaves involute; achenes (1.4-) 1.8-2.4 mm long, either with an elongate beak or a whitish overlay and spongy stipitate base; relatively robust plants, culms 1-7 dm tall; [subgenus Cyperus, section Elegantes]
..2 Scales 6-22, with stout, slightly excurved mucros 0.2-0.3 mm long at apex; achenes black to reddish-brown (1.4-) 1.8-2 mm long × 0.91 mm wide, broadly obovoid, surfaces with a whitish-gray overlay (sometimes sloughing off in age)
..2 Scales 10-20 (-40), with cusps 0.2-0.8 mm ;png, usually narrow, awn-like and recurved at least in the upper scales; achenes brown, 2-2.4 mm long × 0.5-0.8 mm wide, narrowly obovoid
1 Plants not viscid; leaves flat or V-shaped; achenes 0.6-1.5 mm long, without a spongy stipe or whitish overlay, obtuse to apiculate, not beaked; mostly diminutive annuals.
....3 Scales divaricate at maturity, not or barely overlapping, with straight cusps; spikelets held erect-ascending in umbellate to oblong spikes; culms arising singly or slightly cespitose, either with indurate rhizomes to 4 cm or cormose culm bases; [subgenus Cyperus, section Laxiglumi]
......4 Scales 1.3-2.5 mm long, suborbicular, mucronulate (mucro excurrent ≤ 0.2 mm); spikes mostly globose or ovoid, spikelets usually spreading or radiating in all directions (erect-ascending in C. houghtonii); achenes broadly obovoid, ca. 1.5× as long as wide
......4 Scales 2.2-3.2 long, broadly ovate, cuspidate (midrib excurrent (0.3-)0.5-1mm on distal scales); achenes ellipsoid, ca. 2× as long as wide; plants rhizomatous, culms sharply trigonous.
....3 Scales appressed except for excurved cusp (straight in C. nipponicus and C. compressus); spikelets in globose to ovoid clusters or spikes; plants cespitose, annual (perennial in C. acuminatus).
........5 Longest inflorescence bract vertical, appearing as a continuation of the culm; scales with stout, excurved, mucronate apices at most 0.3 mm long; scales with 1 central keel, bicarinate in the basal 1/3, otherwise nerveless or with 2 obscure lateral ribs; [subgenus Pycnostachys, section Luzuloidei]
........5 Longest inflorescence bract ascending; scales with narrow, awnlike cusp (0.3-) 0.5-1 (-1.3) mm long; scales not bicarinate in the basal 1/3, conduplicate to broadly rounded, variously nerved.
..........6 Achenes laterally flattened; scales with greenish midrib, otherwise hyaline, nerveless; cusp 0.3-0.5 mm long; stigmas 2; [rare introduction, FL]; [subgenus Pycreus]
..........6 Achenes trigonous to moderately dorsiventrally compressed; scales weakly to strongly 3-13-nerved; cusp to 1 mm long; stigmas 3 (2 in C. nipponicus).
............ 7 Floral scales weakly 3-9-nerved, laterally greenish to whitish; scale tips with straight to slightly excurved cusp at most 0.7 mm long; achenes broadly obovoid (C. compressus) or oblong-obovoid, dorsiventrally compressed (C. nipponicus).
............ ..8 Achenes broadly obovoid, sharply trigonous; spikelets strongly compressed-quadrangular; cusp 0.5-0.7 mm long, slightly excurved. [widespread]; [subgenus Cyperus, section Compressi]
............ ..8 Achenes narrowly obovoid, planoconvex; spikelets subterete, elliptic in cross-section; cusp < 0.5 mm long, straight; [introduced, NJ, NY]; [subgenus Juncellus; section Pygmaei]
............ 7 Floral scales strongly (5-) 7-13-nerved nearly to the margins, or medially 3-ribbed, often orange to reddish brown laterally at maturity; scale tips with conspicuously excurved cusp 0.5-1 (-1.3) mm long; achenes narrowly ellipsoid to oblong, trigonous.
............ ....9 Scales 3-ribbed medially; spikelets in loose digitate clusters, the rachis essentially absent; achenes 0.5-0.6 mm long, coarsely papillose; [subgenus Pycnostachys]
............ ....9 Scales strongly (5-) 7-13-nerved nearly to margins; spikelets in dense ovoid spikes, rachis obscured by spikelets but well-developed; achenes 0.7-1.2 mm long, puncticulate or minutely papillose; [subgenus Cyperus, section Aristati].
............ ......10 Achenes 0.5-0.6 mm wide, < 2× as long as wide, cuneate to the base; scales 1.0-2.0 mm wide, 9-13-nerved; filaments ca. 2.5 mm long; anthers 0.4-0.8 mm long
............ ......10 Achenes (0.2-) 0.3-0.4 (-0.5) mm wide, > 2× as long as wide, with a minute stipe at the base; scales 0.5-1.0 mm wide, (5-) 7-9 (- 11)-nerved; filaments ca. 1.5 mm long; anthers 0.3-0.4 mm long

Key ZB: Key to Cyperus, subgenus Pycnostachys, section Luzuloidei -- Spikelets in glomerulate heads; scales with midrib bicarinate in basal 1/3, laterally nerveless or 2-ribbed.

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1 Culms triquetrous (sharply trigonous with concave faces), harshly retrorsely scabrid on the angles (very rarely smooth); leaf blades, sheaths and bracts nodulose, with cross-ribs between veins.
..2 Inflorescence congested, primary rays 3-5, secondary and tertiary rays absent; scales ovate, 1.4-1.6 mm long; spikelets 1.5-2.2 mm wide, in dense globose clusters; achenes 1.0-1.2 mm long, < 0.7× as long as the subtending floral scale
..2 Inflorescence broad, diffuse, primary rays 6-12, secondary and often tertiary rays present; scales oblancolate, (1.3-) 1.5-2.0 (-2.4) mm long, spikelets 2-3.2 mm wide, in hemispheric to irregularly globose clusters; achenes 1.2-1.5 mm long, at least 0.7× as long as the subtending floral scale
1 Culms not scabrid on the angles, smooth or slightly scabrous across the faces, obtusely trigonous to nearly terete, rarely with only slightly concave faces; leaf blades and bracts not nodulose.
....3 Bracts 1-3, < 3 mm wide, the largest erect, appearing as a continuation of the culm; culms slender, 1-2 mm in diameter; plants cespitose, fibrous-rooted annuals (perennial in C. reflexus).
......4 Scales yellowish green or straw-colored, sometimes with an orange tinge, apices incurved to straight; stems and rays scabridulous with retrorse prickles, rough to the touch (rarely with only a few prickles); spikelet clusters mostly loosely and irregularly fasciculate.
......4 Scales either dark reddish-brown laterally, often with contrasting green keels or mucronate and conspicuously excurved apically; culms glabrous (rarely scabridulous in C. acuminatus); spikelet clusters densely globose to ovoid or pyramidal.
........5 Scales slightly to strongly excurved apically, mucronate, greenish or stramineous, or sometimes light orange-brown laterally, but this grading evenly into the greenish or yellowish medial portion; achenes papillose, broadly ellipsoid; plants annual, rhizomes absent; heads hemispheric to globose
........5 Scales slightly excurved to incurved apically, acute, deep reddish-brown laterally at maturity, abruptly greenish or yellowish on the keels; achenes rugulose or reticulate, ellipsoid to oblong; plants perennial, rhizomes present (inconspicuous); heads very densely ovoid to pyramidal
....3 Bracts (3-) 6-12, the larger > 3 mm wide, spreading to ascending; culms coarser, 2-5 mm in diameter; plants rhizomatous or cespitose perennials.
..........6 Achene with whitish spongy basal thickening
..........6 Achene without basal thickening.
............ 7 Spikelets elliptic to orbiculate-ovate, ≤ 5 mm long, very densely packed in subglobose, lobulate heads; achenes linear, 4-5× as long as wide, falcate; scales oblong-spatulate, (1.5-) 2-2.5 mm long, apices often excurved
............ 7 Spikelets lanceolate to linear, usually > 5 mm long, heads usually looser; achenes narrowly to broadly ovoid or ellipsoid, not falcate, < 4× as long as wide; scales ovate to lanceolate, to 2 (-2.3) mm long, apices straight to incurved (excurved in C. eragrostis).
............ ..8 Scales declined 60-90 degrees from the rachilla, blunt, incurved; achenes ellipsoid, < 3× as long as wide, narrowed to a distinct stipe; achene surfaces distinctly honeycomb-reticulate, often iridescent
............ ..8 Scales declined 30-45 (-60) degrees from the rachilla; achenes very narrowly ellipsoid, 3-4× as long as wide, stipe absent to poorly developed (ellipsoid with distinct stipe in C. eragrostis); achene surfaces dull, smooth to puncticulate or obscurely reticulate.
............ ....9 Spikelets > 3 mm wide; scales 2-2.3 mm long, excurved apically; heads 20-40 mm in diameter, densely globose, lacking secondary rays; achenes broadly ellipsoid, < 2.5× as long as wide, with a distinct stipe
............ ....9 Spikelets < 3 mm wide; scales < 2 mm long, incurved to straight; heads mostly ≤ 20 mm in diameter, usually with secondary rays; achenes narrowly ovoid or ellipsoid, 3-4× as long as wide, stipe absent.
............ ......10 Culms smooth (or rarely with sparse retrorse prickles); plants robust perennials, with thick deeply set rhizomes; culms mostly >5 dm tall, bases purplish black; floral scales diverging about 30 degrees from the rachilla, pale green; heads usually tightly globose
............ ......10 Culms scabrid (at least apically) with abundant retrorse prickles; plants short-lived cespitose perennials, rhizomes absent; culms mostly < 5 dm tall, bases reddish or brownish; floral scales usually diverging at least 45 degrees from the rachilla, yellowish to yellowish-green; heads mostly loosely and irregularly fasciculate, with flattened spikelets fanned out like a deck of cards

Key ZC: Key to Cyperus, subgenus Pycnostachys, sections Fusci, Diffusi, and Haspani -- Spikelets in digitate clusters or glomerulate heads; scales broadly rounded or conduplicate

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1 Scales orbiculate or broadly obovate, to 1.1 mm long and wide, about as broad as long, minutely mucronate at the tip (“bead-like”); achenes 0.6-0.9 mm long × 0.3-0.4 mm wide, not much exceeded by the scales; plants fibrous-rooted annuals; [sect. Fusci]
..2 Heads very dense, spikelets 30-120 per head; scales 0.6-0.8 mm long × 0.6-0.8 mm wide, greenish; styles 0.1 mm long
..2 Heads looser, spikelets 3-12 per head; scales 0.9-1.1 mm long × 1 mm wide, light brown, bronze, whitish, or purplish brown; styles 0.3-0.4 mm long
1 Scales ovate to lanceolate, (1.1-) 1.6 mm long or longer, mucronate or not; achenes, if < 1.5 mm, much exceeded by (<1/2 the length of) the scales; plants perennial, often with cormose bases, stolons, or rhizomes.
....3 Leave involute; live plants viscid; scales with a mucronate to cuspidate apex at least 0.2 mm long, usually excurved; achenes with beaks 0.5-1.2 mm long or a whitish overlay and spongy stipitate base; [subgenus Cyperus, section Elegantes; keyed here as failsafes]
....3 Leaves flat or V-shaped; live plants not viscid; scales obtuse to acute (minutely mucronate in C. dentatus); achenes at most 1 mm long (longer in the obscurely spicate subg. Cyperus species keyed here as failsafes), without a beak or spongy stipitate base.
......4 Bracts large and conspicuous, 7-11, lanceolate, 5-25 mm wide, the main veins whitish-banded adaxially; inflorescence open and diffuse, often with 2nd and 3rd order rays; [cultivated, rarely naturalizing]; [section Diffusi]
......4 Bracts usually < 7, linear, < 10 mm wide, without whitish banding on the main veins, shorter than the culm.
........5 Spikelets in dense spikes, inflorescence often capitate; scales divaricate at maturity, rounded on the keel, weakly 5-13-nerved; achenes (1-) 1.4-2.5 mm long; plants mostly with hardened cormose culm bases, sometimes also rhizomatous; [dry, sandy habitats]; [subgenus Cyperus, section Laxiglumi; keyed here as failsafes].
........5 Spikelets in loose digitate clusters, rays elongate (except some forms of C. haspan); scales closely appressed, conduplicate and weakly 1-3 (-5)-ribbed; achenes 0.3-1 mm long; plants stoloniferous or rhizomatous; [mostly in wetlands]; [section Haspani]
..........6 Leaf blades usually absent; bracts 2 (-4), usually much reduced; achenes 0.3-0.6 mm long, globose to obovoid.
............ 7 Rays 5-15; anther 1-1.2 mm long; culms hard, not much flattening in pressing; [native]
............ 7 Rays 200-300; anthers 0.3-0.5 mm long; culms soft, terete, flattening in pressing; [cultivated, rarely naturalizing]
..........6 Leaf blades present; bracts 3-5, well-developed and often exceeding the inflorescence; achenes 0.7-1 mm long.
............ ..8 Scales 2-2.5 mm long × 1.2-2 mm wide, ovate or broadly elliptic, 3-26 (-50) per spikelet, minutely mucronate, sometimes excurved; spikelets ovate to linear, straight, light brown to reddish-brown laterally with greenish midribs; plants with stolons terminated by tubers, and often proliferous spikelets
............ ..8 Scales 2.5-3 mm long × 1-1.8 mm wide, relatively narrowly ovate-elliptic, 20-60 per spikelet, blunt and incurved; spikelets lanceolate to linear, often contorted, pale yellowish at maturity; plants with stolons, lacking tubers or proliferous spikelets

Key ZD: Key to Cyperus, subgenus Cyperus -- Spikelets quadrangular to subterete; scales 1-8, persistent rachillas deciduous, articulate at the base

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1 Culms, rays, and leaves bluish-glaucous, papillose; leaves harshly scabrid on margins and midrib; spikes with numerous well-developed branches or secondary rays; spikelets dark reddish brown at maturity
1 Culms, rays, and leaves green, not papillose; leaves glabrous to scabridulous; spikes solitary or with a few reduced basal branches; spikelets various.
..2 All but the uppermost spikelets strongly (-weakly in some forms of C. hystricinus) reflexed; scales (3.8-) 4-4.9 (-5.4) mm long, terminal involute and prolonged distally, midrib often bent downward; achenes linear to linear-oblong, (2.2-) 2.5-3 (-2.3) mm long; [section Umbellati, subsection Longistylis, C. retrofractus complex]
....3 Spikes mostly at least 2× as long as wide, slightly (or not) narrowed to base, spikelets reflexed to spreading; culms, leaves, and bracts glabrous except for marginal prickles on leaves and bracts; rachilla wing clasping achene for its entire length (concealing it in abaxial view); floral scales golden-brown when mature
....3 Spikes mostly about as long as wide and strongly narrowed to the base, spikelets reflexed; culms scabrous, bracts scabridulous and also often hirtellous; rachilla wing clasping achene for <3/4 its length; floral scales greenish to brown or reddish-purple-striped.
......4 Rays scabrid throughout their lengths; leaves and bracts puberulent; longest ray equal to or longer than the longest bract; culms roundly trigonous to subterete; terminal scale spinose distally; scales 1-2 (-3); spikes tight, burlike, turbinate
......4 Rays glabrous or rarely with a few hairs just below the spike; leaves and bracts with hairs confined to abaxial midrib; longest ray shorter than longest bract; culm sharply trigonous; terminal scale involute but not spinose; scales (2-)3-6; spikes often loose, sometimes more elongate
..2 Spikelets ascending to spreading, or reflexed in the lower half of spike; scales 1.8-5.3 mm long, terminal scale not modified as above; achenes ellipsoid to narrowly oblong, 1.2-2.4 (-2.6) mm long (linear-oblong in C. refractus).
........5 Spikes densely cylindric, all sessile or 1-3 (-5) lateral spikes on short horizontal rays; spikelets ellipsoid (rarely oblong-ellipsoid), with 1-2 (-4) scales; [section Umbellati, subsection Brevistyli].
..........6 Spikes dense, the rachis obscured when pressed; achenes lacking a stipitate base, apiculate at the apex; [native of Mexico and Central America, introduced northward along the Gulf and Atlantic coasts]
..........6 Spikes relatively loose, the rachis usually visible when pressed; achenes cuneate to a stipitate base, broadly rounded to acute at the apex; [native, s. TX, uncertain reports]
........5 Spikes oblong to ovoid (cylindric in C. tetragonus), primarily on well-developed rays; spikelets oblong-lanceoloid to linear, with (1-) 2-8 scales.
............ 7 Spikelets very closely spaced, obscuring the rachis in life and when pressed; [section Umbellati, subsection Brevistylis]
............ ..8 Spikes broadly and appearing (because of longer spikelets) relatively loosely ellipsoid to ovoid-cylindric, 2.5-7 cm long × 1.5-6 cm wide; spikelets (11-) 12-25 (-28) mm long; achenes 2.2-3 mm long (if < 2.5 mm long, noticeably falcate).
............ ....9 Spikes dense, ellipsoid to obovoid, convex, with 50-90 spikelets; scales 3-6 (-7), each 4-4.6 mm long, not red-purple striate; achenes 3-4× as long as wide, falcate
............ ....9 Spikes loose, broadly ovoid or ellipsoid to ovoid-cylindric, with 13-75 spikelets; scales 4-8(-11), each 4.5-5.3 mm long, red-purple striate; achenes 4-5× as long as wide, straight
............ ..8 Spikes tightly globose or to oblong, not more than 2.5 cm long or 2 cm wide; spikelets 2-8 mm long; achenes < 2.3 mm long, straight.
............ ......10 Spikes uniformly convex throughout, globose or globose-ellipsoid, so dense as to appear nearly smooth in silhouette; scales 3.5-4.6 (-4.8) mm long, acute
............ ......10 Spikes cylindric, oblong, ellipsoid, or ovoid, mostly less dense; scales 1.8-3.6 mm long (or, if longer, mucronate).
............ ........11 Terminal scale of spikelet reduced, sterile, involute, with a minute but distinct mucro to 0.3 mm long, usually uncinate (hooked); fertile scales (if more than one) not overlapping on the same side of the rachilla, usually red-brown or orangeish laterally at maturity; leaf blades 1-3 mm wide; [Cyperus retroflexus complex]
............ ..........12 Fertile floral scales 1.9-3.0 (-3.3) mm long; rachilla wing usually membranaceous throughout; rachilla lacking lateral nerves; longest spikelets 2.8-5.8 (-8.0) mm long; terminal sterile floral scale of spikelet often much reduced, less than 2/3 the length of fertile floral scales; longest peduncle less than 2.7 (-3.9) cm long; plants diminutive, culms 3-35 (-45) cm tall
............ ..........12 Fertile floral scales (2.8-) 3.0-3.9 mm long; rachilla wing usually chartaceous beyond clasped achene angle, border membranaceous; rachilla with two lateral nerves, one along each side of the median; longest spikelets 4.9-9.0 (-11.3) mm long; terminal sterile floral scale usually not greatly reduced, 2/3 or more the length of fertile floral scales; longes peduncle (0.5-) 2.4-6.8 cm long; plants more robust, culms usually >25 cm tall
............ ........11 Terminal scale of spikelet not differentiated; scales acute, greenish-hyaline to brownish or straw-colored laterally; scales overlapping; leaf blades 1.5-5 mm wide.
............ ............ 13 Spikes relatively loosely ovoid, 8-20 mm wide, with (5-) 10-50 (-70) spikelets, lacking basal branches; spikelets (2.2-) 3.5-10 mm long, angular in ×-section, greenish-hyaline to pale yellow-green; bracts horizontal
............ ............ 13 Spikes densely oblong-ellipsoid to ovoid, 6-8 (-10) mm wide, with (13-) 30-200 (-274) spikelets, occasionally with short basal branches; spikelets 2.2-4 (-4.5) mm, subterete, straw-colored to brown at maturity; bracts horizontal or ascending to erect; [Cyperus retrorsus complex]
............ ............ ..14 Achenes oblong-fusiform, stipitate, narrowed to both ends; spikes densely oblong to oblong-cylindric, often 3× or more as long as wide; scales ascending (the tips free), usually straw-colored; bracts horizontal
............ ............ ..14 Achenes oblong, usually abruptly constricted at the ends; spikes ovoid to oblong, to 2× as long as wide (rarely longer in C. retrorsus); scales appressed, usually reddish-brown at maturity; bracts ascending to erect (sometimes horizontal in C. nashii).
............ ............ ....15 Spikes > 1.5× as long as wide, each with (42-) 50-200 (-274) spikelets; achenes 0.4-0.5 (-0.6) mm wide; stems moderately cespitose; [widespread and weedy]
............ ............ ....15 Spikes < 1.5 × as long as wide, each with (13-) 30-92 spikelets; achenes 0.5-0.7 mm wide; stems single to slightly cespitose; [Florida scrub, northward and westward in coastal dunes]
............ ............ ......16 Rays 8-27; anthers 0.8-1.0 mm long; achenes 1.6-1.7mm long × 0.6-0.7 mm wide
............ ............ ......16 Rays 3-6 (-8); anthers 0.2-0.5 (-0.7) mm long; achenes 1.3-1.6 mm long × 0.5-0.6 mm wide
............ 7 Spikelet attachments spaced apart at least proximally, rachis not obscured when pressed and usually also visible in life.
............ ............ ........17 Fertile floral scales 1-3 (-5), not overlapping on the same side of the spikelet (if more than one); terminal scale reduced, sterile and involute, mucro usually uncinate; achenes (1.7-) 1.9-2.6 mm long; [section Umbellati, Cyperus retroflexus complex]
............ ............ ..........18 Longest spikelets 10-21 mm long, strongly contorted; distal scales with scabrid midrib and mucro 0.6-1.9 mm long; longest floral scale of spikelet (3.5-) 3.7-4.8 mm long; anthers 0.5-1.3 mm long; achenes > 3× as long as wide; [TX]
............ ............ ..........18 Longest spikelets usually < 10 mm long, at most somewhat flexuous with curved tips; distal scales with glabrous midrib and mucro 0.1-0.3 (-0.5) mm long; longest floral scale of spikelet (2.1-) 2.5-3.5 (-4.0) mm long; anthers 0.3-0.5 (-0.6) mm long; achenes 2-3 (-3.3)× as long as wide; [more widespread]
............ ............ ........17 Fertile floral scales 3-8, reaching the next scale or overlapping on the same side of the spikelet; terminal scale not involute and sterile, mucro straight; achenes various.
............ ............ ............ 19 Scales 3.2-5.3 mm long, acute; spikes broadly ovoid-cylindric to ellipsoid, spikelets 5-30mm long; achenes narrowly oblong to linear, 3-6× as long as wide; culm bases cormose.
............ ............ ............ ..20 Spikelets ±terete; scales 4.5-5.3 mm long, persistent, laterally reddish brown or tinted with reddish brown if paler and stramineous; achenes usually at least half as long as floral scale; achenes linear-oblong, 2.6-3 mm long, 5-6× as long as wide, > 0.5 mm wide; anthers 1-1.5 mm long; spikes usually broadly and convexly ellipsoid or ovoid, usually unbranched (or rarely with 1-2 reduced proximal branches); [section Umbellati, subsection Brevistylis]
............ ............ ............ ..20 Spikelets flattened; scales 3.2-4.5 (-6) mm long, laterally golden yellow to stramineous; achenes less than half as long as floral scale; achenes oblong, (1.5-) 1.8-2.4 mm long, 3-4× as long as wide, < 0.4 mm wide; anthers 0.3-0.5 mm long; spikes usually parallel-sided, ovoid-cylindric, frequently branched; [section Strigosi]
............ ............ ............ ....21 Plants annual, 2-3 dm tall; culm 0.5-1 (-1.5) mm in diameter; floral scales with excurved aristate apex
............ ............ ............ ....21 Plants perennial, ≥ 3 dm tall; culm 1.8-3 mm in diameter; floral scales not aristate
............ ............ ............ ......22 Plants > 10 dm tall; floral scales more loosely arranged, the tips gaping distally
............ ............ ............ ......22 Plants 3-8 (-11) dm tall; floral scales appressed to slightly gaping distally
............ ............ ............ 19 Scales (2-) 2.5-3.2 (-4) mm long, acute to cuspidate; spikes narrowly cylindric to ovoid, spikelets mostly 4-8mm long (if longer, scales mucronate); achenes ellipsoid, 2-3× as long as wide; culm bases not cormose.
............ ............ ............ ........23 Spikelets ellipsoid, 2-4× as long as wide; achenes ellipsoid; spikes narrowly cylindric, 4-13 mm wide; [section Tetragoni]
............ ............ ............ ........23 Spikelets oblong to linear, 4-10× as long as wide; achenes ellipsoid to narrowly oblong; spikes narrowly to broadly cylindric to oblong or ellipsoid, ≥ 12 mm wide (C. retroflexus occasionally as narrow as 8 mm wide, but not cylindric).
............ ............ ............ ..........24 Floral scales pale olivaceous to yellowish, not mucronate (rarely with a mucro to 0.1 mm long); spikes cylindric, loose, 6-10 spikelets per 5 mm span of the rachis; culms 0.5-1 mm in diameter; leaves 0.8-2.3 (-3) mm wide; [more widespread]; [section Tetragoni]
............ ............ ............ ..........24 Floral scales straw-colored to reddish-brown, acute or mucronate, mucro up to 0.2 mm long; spikes loosely to densely ovoid to oblong, spikelets 8-21 per 5 mm span of the rachis; culms 1-2.6 mm in diameter; leaves (1-) 3-6 (-10) mm wide; [TX].
............ ............ ............ ............ 25 Floral scales not mucronate; spikes mostly narrowly oblong (usually 2× or more as long as wide); rachis, spikelets, bracteoles, peduncles, and prophylls not reddish brown striate or maculate (at 10× magnification); [section Tetragoni]
............ ............ ............ ............ 25 Floral scales mucronate, mucro at least 0.2 mm long; spikes densely ovoid to loosely ellipsoid-oblong (to 1.5× as long as wide); rachis, spikelets, bracteoles, peduncles, and prophylls usually conspicuously reddish brown striate or maculate (at 10× magnification); [section Strigosi].
............ ............ ............ ............ ..26 Spikes loose, spikelets 8-12 per 5 mm span of the rachis, divaricate; scale color not bilaterally variable, scales yellowish to light brown; spikelets stipitate, stipe 0.3-0.5 mm long; spikes oblong to cylindric
............ ............ ............ ............ ..26 Spikes denser, spikelets 11-21 per 5 mm span of the rachis (at least in the upper portion), often the upper spikelets ascending; scale color bilaterally variable, reddish or reddish-brown to whitish; spikelets estipitate or stipe to 0.2 mm long; spikes ellipsoid to oblong

Key ZE: Key to Cyperus, subgenus Cyperus of various affinities -- Spikelets compressed; scales deciduous or persistent; rachilla persistent or deciduous after the scales

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1 Culms and leaves bluish-glaucous in life; scales overlapping, slightly spreading, glossy reddish brown at maturity; plants cespitose perennials; [FL; beaches, dunes, coastal rock]
..2 Rays absent, inflorescence a single globose spike, rachis only 1-3 mm long; scales 1.5-2.2 mm long; achenes 1-1.2 mm long, glabrous, puncticulate, or papillose; leaves and bracts 1-2.5 mm wide; culms 0.5-1 mm in diameter; [section Laxiglumi]
..2 Rays present, inflorescence of multiple well-developed spikes, though often very congested; scales 2.5-3 mm long; achenes 1.3-2 mm long, coarsely punctate; leaves and bracts (1.5-) 3-10 mm wide; culms 0.8-2.6 mm in diameter; [section Thunbergiani]
1 Culms and leaves green, not glaucous; scales divaricate to closely imbricate, mostly greenish, light brown, or straw-colored (except C. rotundus and C. setigerus); [more widespread].
....3 Rachilla wingless (except C. prolixus and C. grayi); spikelets at maturity 2-4 mm wide, scales divaricate (the spikelet appearing coarsely serrate in outline).
......4 Rachis hispidulous; spikes loosely oblong-ovoid, with spikelets spreading, the elongate, well-developed rachis clearly visible; scales 1.8-2 mm long, light brown to yellowish; achenes 1-1.2 mm long; [sect. Proceri]
......4 Rachis glabrous; spikes densely ovoid or globose, or umbellate to oblong, the rachis elongate to nearly absent; scales 1.8-3.2 mm long; achenes 1.5-2.4 mm long (1-1.2 mm long in C. cephalanthus).
........5 Rays compressed; plants robust, up to 2m tall; inflorescence diffuse, 2nd-order rays present, erect, 1-10 cm long, usually bearing well-developed 3d-order rays 0.5-5 cm long; [sect. Distantes]
........5 Rays terete to trigonous; plants mostly less robust, to 1m tall; inflorescence more compact, 2nd- and 3rd-order rays absent or poorly developed.
..........6 Plants robust, culms 40-100 cm tall, sharply trigonous, scabrid to hirtellate on the angles; spikes very densely ovoid, with 25-50+ spikelets, subtended by well-developed secondary bracts and often branched at the base; achenes 1.0-1.2 mm long, ellipsoid, <1/2 as long as the scales; [coastal prairies; LA, TX]; [sect. Thunbergiani]
..........6 Plants smaller, culms to 50 cm tall, terete to trigonous, not scabrid (except C. schweinitzii); spikes relatively loose, with 3-24 spikelets, unbranched and lacking secondary bracts; achenes 1.5-2.2 mm long, mostly ≥ 1/2 as long as the scales; [dry, sandy or rocky soils; collectively widespread]; [sect. Laxiglumi].
............ 7 Inflorescence bracts deflexed (to horizontal); spikelets in a single sessile hemispheric to globose capitate cluster, or with an additional 1-4 smaller pedunculate spikes, these densely globose with an obscure rachis < 6 mm long; [Cyperus lupulinus complex]
............ ..8 Anthers 0.8-1 mm long; achenes 0.5-0.8 mm wide, narrowly oblong; scales usually yellowish to yellowish brown; leaves very narrow, 0.5-2 mm wide
............ ..8 Anthers 0.3-0.6 mm long; achenes 0.8-1.2 mm wide, ±ellipsoid; scales usually off-white to pale tan to light reddish brown; leaves often broader, 1-4 mm wide.
............ ....9 Scales 2.5-3.8 mm long, usually fitting loosely over the mature achene, the margins spreading or loosely clasping it; spikelet with 5-22 scales
............ ....9 Scales 1.8-2.5 mm long, usually fitting tightly over the achene, the margins tightly clasping it; spikelets with 3-7 scales
............ 7 Inflorescence bracts horizontal to erect; spikes primarily pedunculate, loosely globose, densely ovoid, or more elongate.
............ ......10 Scales 2.2-3.2 mm long with a conspicuous cusp > 0.3 mm long (at least on the distal scales); body of scale 2.2-3.2 mm long; spikes umbellate to oblong, spikelets all erect-ascending; achenes 2-2.4 mm long, ellipsoid; plants rhizomatous, culms sharply trigonous
............ ......10 Scales 1.3-2.5 mm long, acute or minutely mucronate (mucro ≤ 0.2mm long); spikes mostly globose or ovoid, spikelets usually spreading or radiating in all directions (erect-ascending in C. houghtonii); achenes 1.5-2.4 mm long; plants various.
............ ........11 Spikelets mostly erect-ascending, the spikes umbellate to broadly ovoid; scales with distinct mucro 0.1-0.2 mm long; achenes 1-1.5 mm wide, broadly ellipsoid; anthers 0.5-0.7 mm long
............ ........11 Spikelets radiating in all directions, the spikes globose or subglobose; scales acute; achenes 0.7-1.2 mm wide, narrowly ellipsoid or oblong-ellipsoid; anthers 0.7-1.2 mm long.
............ ..........12 Rachilla winged, wings 0.6 mm wide; achenes 1.5-2 mm long × 0.7-1 mm wide; scales 2-2.8 mm long; anthers 0.7-1 mm long; [Atlantic coast, south to AL]
............ ..........12 Rachilla wingless; achenes 2-2.4 mm long × 0.9-1.2 mm wide; scales 2.5-3 mm long; anthers 1-1.2 mm long; [Midwest south to LA]
....3 Rachilla winged, wings at least 0.4 mm wide; spikelets at most 2.2 mm wide, scales overlapping, tips closely imbricate, the margin appearing smooth or slightly serrate (some forms of C. strigosus have looser scales).
............ ............ 13 Scales 1-1.5 mm long, deciduous; spikes cylindric, with (20-) 40-80+ spikelets, often with secondary rays; fibrous-rooted annuals, but often robust, roots reddish; [sect. Fastigiati]
............ ............ 13 Scales 1.8-4.5 (-6) mm, deciduous or persistent; spikes ovoid, with (2-) 3-50 spikelets; stoloniferous, rhizomatous, cormose-based, or (C. sphacelatus) cespitose perennials.
............ ............ ..14 Plants with cormose culm bases; scales 3.2-4.5 (-6) mm, 3-11 per spikelet, pale greenish-brown to straw-colored, dull; spikelets strongly compressed (at maturity), the scales loosely overlapping, tips spreading; achenes narrowly oblong, (1.5-) 1.8-2.4 mm long; [section Strigosi]
............ ............ ..14 Plants lacking cormose culm bases; scales 1.8-4 (-4.4) mm long, 6-36 (-42) per spikelet, various; spikelets often only slightly compressed, scales closely imbricate, tips appressed; achenes ellipsoid to oblong, 1.1-2 mm long.
............ ............ ....15 Scales pale greenish-white, deciduous, usually with dark-speckled margins visible as a prominent dark line on each side of the spikelet; plants fibrous-rooted; anthers 0.6mm long, styles 0.6-1.2 mm long, stigmas 1-1.4 (-1.7) mm long; [rare introduction, FL]; [section Subimbricati]
............ ............ ....15 Scales pale yellowish to brown or deep purple, persistent or deciduous; plants with well-developed rhizomes or stolons; anthers 1-2.5 mm long, styles (0.7-) 1-3.6 mm long, stigmas (1.2-) 1.8-6 mm long; [collectively widespread]; [section Cyperus].
............ ............ ......16 Culms terete at least towards the base, nodose-septate, with internal partitions every 5-50 mm, more frequent upwards; leaves usually all reduced to bladeless sheaths; bracts 2 (-4), erect, reduced, mostly < 2 cm long
............ ............ ......16 Culms trigonous to rounded-trigonous, not nodose-septate; leaf blades present; bracts (2-) 3-8, spreading to ascending, well-developed.
............ ............ ........17 Scales deciduous, (2.2-) 2.7-4.5 (-6) mm, mostly reddish-brown; robust perennials 5-10dm tall from thick, indurate rhizomes, lacking tubers; achenes maturing, oblong
............ ............ ........17 Scales persistent, 1.8-3.4 mm long, mostly yellowish or dark glossy purplish; plants mostly 1-6 dm tall (rarely taller in C. esculentus), with slender stolons 1-2 mm in diameter, these producing terminal tubers; achenes ellipsoid or not maturing.
............ ............ ..........18 Spikelets (2-) 3-14 per spike, bracts often not exceeding the inflorescence; scales glossy dark purplish, with green keels and hyaline border; culm bases indurate, stolons wiry, horizontal, 1-2 mm in diameter, producing irregular, often elongate tubers
............ ............ ..........18 Spikelets (3-) 10-28 per spike, bracts exceeding the inflorescence; scales yellowish to dull reddish-brown; culm bases not indurate, stolons spongy, weak, 1 mm in diameter, producing globose tubers; [Cyperus esculentus complex].
............ ............ ............ 19 Spikelets ascending-erect; floral scales deltate-ovate, widest 1/4-1/3 of the way from the base
............ ............ ............ 19 Spikelets spreading; floral scales ovate to ovate-lanceolate, widest near the middle.
............ ............ ............ ..20 Style and stigma combined < 4.2mm long; floral scales 1.8-2.7 mm long; anthers (1-) ca. 1.3 (-1.6) mm long
............ ............ ............ ..20 Style and stigma combined > 4.2mm long; floral scales (2.7-) 2.9-3.4 mm long; anthers (1.2-) 1.3–2.1 mm long
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