Flora of the Southeastern United States
2022 Edition


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

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