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

Cyperaceae

Cyperus

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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, 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
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Key to Cyperus, 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 sharply trigonous in cross-section (the faces concave), and harshly 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 obtusely trigonous in cross-section (faces usually convex), not scabrid on the angles, sometimes scabrous across 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 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