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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. |