Lacustris: 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 3; achenes three-sided, occasionally terete, though their shape may be concealed by flattened perigynia.  NOT [Stigmas 2; achenes lenticular.]
	Spikes 2 or more per culm, terminal and lateral; spike bracts present on lateral spikes (except in Section Phyllostachyae), lowest bract usually evident, often conspicuous.  NOT [Spikes 1 per culm, terminal; spike bracts absent.]
	Lower pistillate scales not bract-like or leaf-like but similar in size and shape to individual perigynia (up to twice as long as perigynia in C. magellanica ssp. irrigua).  NOT [Lower pistillate scales resembling green, leaf-like bracts much longer and wider than individual perigynia.]
	Perigynia glabrous (i.e. lacking pubescence). NOT [Perigynia sparsely to densely pubescent or puberulent (in C. pedunculata pubescence represented by very short hairs scattered near tip; in some species of Sect. Acrocystis, perigynia may be glabrous or virtually hairless, but all members of this group have convexly 3-sided to terete achenes with tight-fitting perigynia and a stipe-like base about equal to beak in length).]
	Beak over 0.5 mm long and usually visibly bidentate (teeth hyaline in C. sprengelii, inconspicuous in C. viridula, very short in C. oligosperma).  NOT [Beak absent or less than 0.5 mm long; if more than 0.5 mm long, then terminating in an orifice without teeth.]
	Style continuous with achene and persisting at maturity as a long, curved or straight prong. NOT [Style jointed at base and deciduous from achene, if present at maturity, breaks of readily when manipulated.]
	Perigynia shorter and usually wider, usually at most only 4 times longer than wide; staminate spikes much longer than individual perigynia; mostly common species. NOT [Perigynia long and narrow, (8.7) 10-12.5 mm long, 1.5-2 mm wide, about 6 times longer than wide with long tapering tip; staminate spike about same size, or smaller than, perigynia adjacent to it; rare northern species.]
	Perigynia 20-200 per spike; leaves wider, not wiry; pistillate spikes 2-6, most separate to overlapping. NOT [Perigynia 5-15 per spike; leaves 0.5-2.5 mm wide, involute, wiry; pistillate spikes few (1-2), remote (or upper overlapping with staminate spike).]
	Lower pistillate spikes short-stalked or sessile, erect to ascending; lower part of pistillate scales more substantial, usually wider than 1 mm with awn shorter than lower part although those at base of spike can be narrower and long awned. NOT [Pistillate spikes on filiform stalks, erect or often nodding; lower part of pistillate scales throughout spike not much more than hyaline wings along bottom of long awn and no wider than 1 mm.]
	Style base straight or somewhat bent; perigynia 12-26 nerved; ventral strip disintegrating into laddered fibers with age.  NOT [Style base contorted in an S shape; perigynia 6-15 nerved; ventral strip membranous, not disintegrating into laddered fibers with age.]
	Beak 0.5-1.6 mm long; leaves 5-10 (21) mm wide; teeth to 0.7 (0.9 fna) mm long, straight.  NOT [Beak 2-3 (4) mm long; leaves 2-8 (10) mm wide; teeth 0.8-3 mm long, straight, spreading or outwardly-curved.  Section Carex (C. atherodes, C. laeviconica).]