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

Cyperaceae

Cyperus

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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]
                            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
                                  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].