1. Lowest spike pendant.
            2. Female spikes truncate at base, 5–7 mm wide; perigynia 1.6–2.5 mm wide, yellow–brown,      leathery, stipitate; fruit dull, constricted; mostly saline or brackish wetlands                                                                              ---- C. lyngbyei
            2. Female spikes acute at base, 4–5 mm wide; perigynia 1.0–1.2 mm wide, pallid–brown, papery, sessile; fruit glossy, not constricted; fresh wetlands                                                                                                                                                                                      ---- C. sitchensis (C. aquatilis var. dives)

1. Lowest spike erect or spreading.
       3. Stem round or very obtusely angled, smooth; scales sometimes scabrous-awned; perigynium beaks conical; lowest bract often spathe-like and enclosing spike; saline or brackish wetlands.
            4. Leaves filiform–involute, 1–2 mm wide, rounded on the back, with the midvein inconspicuous and smooth; fertile stems less than 15 (–28) cm tall (vegetative shoots can be taller)                                                                ---- C. subspathacea
            4. Leaves flat to folded, 2–5 mm wide, with a conspicuous, ± scabrous midvein; plants (15–) 20–50 cm tall                                                                                                                                                                                         ---- C. ramenskii
       3. Stem clearly triangular, angles acute or obtuse, scabrous or smooth; scales not scabrous-awned; perigynium beaks cylindrical; lowest bract not spathe-like and not enclosing spike; fresh wetlands.
              5. All spikes strongly overlapping, inflorescence dense, ± head-like; terminal spikes usually gynecandrous.
                  6. Perigynia ovate, with 5–7 nerves on each face, stipe to 0.5 mm        
                                                                         ---- C. enanderi (C. lenticularis var. dolia)
                  6. Perigynia elliptic, with 0–5 nerves on each face, stipe to 0.2mm                                                                           ---- C. eleusinoides
              5. At least the lowermost spikes ± separate, not notably overlapping with the terminal, inflorescence more open; terminal spike usually staminate.
                     7. Perigynia nerved on both faces, distended at base, stipitate, tightly enclosing fruit; basal sheaths lacking reddish or purplish color                                                                                                                                ---- C. kelloggii (C. lenticularis)
                     7. Perigynia essentially nerveless on the faces, not distended at base, ± sessile, loosely enclosing fruit; basal sheaths usually reddish or purplish tinged.
                        8. Lowest bract longer than the inflorescence; pistillate spikes 3–7, 3–10 cm        
                                                                         ---- C. aquatilis
                        8. Lowest bract ± equal to or shorter than inflorescence; pistillate spikes 2–3, 1–3 cm long.                                                      

                                                                         ---- C. bigelowii subsp. lugens