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| 1 Terminal spike staminate; lateral spikes staminate, androgynous, or pistillate; base of culms tan, brown, or ivory. |
| ..2 Plants without rhizomes or with very short ones, densely cespitose |
| ..2 Plants with short-creeping rhizomes, loosely cespitose or colonial |
| 1 Terminal spike staminate or gynecandrous; lateral spikes pistillate, gynecandrous or rarely distal spike staminate; base of culms usually covered with dark maroon bladeless sheaths (often missing or very short in C. prasina). |
| ....3 Perigynia 2-ribbed but otherwise veinless or nearly so, green to yellow at maturity |
| ....3 Perigynia 2-ribbed and veined between ribs, often conspicuously so, green to olive-green at maturity, usually red dotted. |
| ......4 Perigynia fusiform to narrowly lance-ovoid, > 5 mm long, including the elongate beak; leaves generally < 5 mm wide; leaf sheaths usually glabrous, at least on back |
| ......4 Perigynia ovoid-oblong to lance-ovoid, 2-6 mm (mostly < 5 mm long) tapering to a beak shorter than the body or beakless; leaves 2.5-12 mm wide; leaf sheaths glabrous or pubescent. |
| ........5 Terminal spike usually gynecandrous, rarely staminate |
| ........5 Terminal spike usually staminate, rarely gynecandrous. |
| ..........6 Lateral pistillate spikes erect at maturity, narrowly oblong to cylindric, to 25 × 2.5–9 mm, on stiff peduncles |
| ..........6 Lateral pistillate spikes drooping at maturity, short cylindric to linear, 8-80 × 3-5 mm, on slender arching peduncles |