| | 1. Stem 1; stolons with tubers; fruit seldom maturing |
| |
| | 2. Flower bracts yellow-brown to brown |
| C. esculentus |
| | 2' Flower bracts ± dark red to purple |
| C. rotundus |
| | 1' Stems generally > 1, clumped or not; stolons, tubers 0; fruit maturing |
| |
| | 3. Fruit lenticular; stigmas 2 |
| |
| | 4. Fruit face next to spikelet axis |
| C. laevigatus |
| | 4' Fruit angle next to spikelet axis |
| |
| | 5. Annual; rhizomes 0; spikelets in open spikes; flower bracts brown or ± red-brown; fruit (ob)ovoid, black |
| C. bipartitus |
| | 5' Perennial; rhizomes short; spikelets generally in head-like spikes; flower bracts light brown to black; fruit ovoid to elliptic, brown |
| C. niger |
| | 3' Fruit 3-angled; stigmas 3 |
| |
| | 6. Tip of flower bract outcurved, narrowly acute or bristle-like |
| |
| | 7. Flower bract 3-veined; fruit widest ± near middle |
| C. acuminatus |
| | 7' Flower bract 5–11-veined; fruit widest just below tip |
| C. squarrosus |
| | 6' Tip of flower bract not outcurved, acute, obtuse, or rounded, sometimes with small point but not bristle-like |
| |
| | 8. Basal leaf blades 0; inflorescence bracts (10)14–22 |
| C. involucratus |
| | 8' Basal leaf blades present; inflorescence bracts 1–12 |
| |
| | 9. Flower bract < 1.1 mm; annual; rhizomes 0 |
| |
| | 10. Spikelets 50–100+ in dense heads |
| C. difformis |
| | 10' Spikelets 3–15 in open heads |
| C. fuscus |
| | 9' Flower bract 1.3–4 mm; annual or perennial herb; rhizomes generally present |
| |
| | 11. Fruit body ± as long as wide, stalked |
| C. eragrostis |
| | 11' Fruit body 1.5–3 × longer than wide, ± sessile |
| |
| | 12. Spikelets flat; flower bract reddish |
| C. parishii |
| | 12' Spikelets slightly flat or subcylindric; flower bract brown, light reddish brown, or yellowish |
| |
| | 13. Stem densely bumpy or warty; spikelets in dense, cylindric spikes |
| C. ligularis |
| | 13' Stem smooth; spikelets in open, ovoid to cylindric spikes |
| |
| | 14. Flower bract 1.3–1.5 mm; fruit 0.7–1 mm |
| C. erythrorhizos |
| | 14' Flower bract 2–4 mm; fruit 1.5–2.4 mm |
| |
| | 15. Annual; stem base not corm-like; flower bract persistent, light brown splotched reddish, midvein green; spikelet axis jointed at each bract, spikelet falling apart |
| C. odoratus |
| | 15' Perennial; stem base corm-like; flower bract yellowish, persistent or not; spikelet axis continuous, spikelet falling as unit |
| C. strigosus
|