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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.

Cyperaceae

Cyperus

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