Aquatilis: Answers to key questions in Sedges (Carex) of Saskatchewan, Fascicle 3, Flora of Saskatchewan by Anna Leighton leading to this species. The answers are in the order you would normally work through the key. 

	Stigmas 2; achenes lenticular.  NOT [Stigmas 3; achenes three-sided, occasionally terete, though their shape may be concealed by flattened perigynia.]
	Spikes 2 or more per culm, terminal and lateral; spike bracts present on lateral spikes; lowest spike bracts usually evident, often conspicuous, even in compact heads composed of densely bunched and indistinguishable spikes (except in C. maritima, C. chordorrhiza and C. microptera).  NOT [Spikes 1 per culm, terminal; spike bracts absent]
	Individual spikes distinguishable in an open inflorescence (densely bunched in C. bicolor); spikes in any one inflorescence either markedly different in appearance (with terminal spike staminate and lateral spikes pistillate), or subtly different in appearance (with terminal spike gynecandrous and lateral spikes pistillate), sessile or stalked.  NOT [Individual spikes distinguishable in an open inflorescence, or indistinguishable in a compact head; spikes in any one inflorescence alike in appearance due to their similar composition (i.e. all are gynecandrous, androgynous, pistillate or staminate), sessile.]
	Perigynia not filled with spongy tissue at base. NOT [Spongy tissue visibly filling bottom one-third to one-half of the perigynium with achene positioned above it; perigynia less than 4 mm long.  Section Stellulatae (C. echinata, C. interior, C. sterilis)]
	Beak absent or a short tube to about 0.2 mm long and lacking teeth; style deciduous from achene and if present at maturity breaks off readily when manipulated; widely distributed or rare species. NOT [Beak 0.2-0.5 mm long, bidentate; style base continuous with achene and persisting as a prong; rare species of far north.]
	Terminal spike(s) staminate (may have occasional pistillate flowers at tip or base); perigynium surface shiny or dull but not powdery, +/- flattened in cross-section; beak a short tube 0.1-0.2 mm long.  Section Phacocystis (C. aquatilis, C. bigelowii, C. lenticularis).  NOT [Terminal spike staminate or gynecandrous; perigynium surface appearing powdery due to a coating of minute papillae, (becoming smooth at maturity in C. aurea), inflated except in C. bicolor, beakless.  Section Bicolores (C. aurea, C. bicolor, C. garberi).]
	Culms 4-12 dm tall or rarely shorter; leaves 2-8 mm wide; terminal predominately-staminate spikes 2-4; perigynia usually obovate, rhizome 2-5 mm wide.  NOT [Culms rarely taller than 4 dm; leaves 2-3 (4) mm wide; terminal predominately-staminate spikes 1-2; perigynia elliptic or ovate; rhizome absent or 2-3 mm wide.]