Carex cristatella
 
Crested Sedge

Base of Sterile Leaf, Adaxial Side

Hudson Bay Regional Park
02-August-2016

The leaf sheaths are loose and somewhat winged on one or both sides.  When manipulated, the leaf sheaths can be moved with respect to the underlying culm.  The wings are thin flaps that can be easily bent back and forth.  These features are probably best seen in cross section (see other photos).

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Cristatella: 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. 
bulletStigmas 2; achenes lenticular. NOT [Stigmas 3; achenes three-sided, occasionally terete, though their shape may be concealed by flattened perigynia.]
bulletSpikes 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]
bulletIndividual 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.  NOT [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.]
bulletCulms loosely to densely cespitose (occasionally mat-forming rather than in discrete clumps); rhizomes, if present, usually short with culms arising close together along them.  NOT [Culms single, or a few together, well-spaced along conspicuous rhizomes or stolons.]
bulletSpikes gynecandrous, (terminal spikes may be staminate in SK material of C. mackenziei; pistillate or staminate spikes occur in Sect. Stellulatae, a group distinguished by spongy tissue filling lower one-third to one-half of the perigynium); if heads have indistinguishable spikes, the heads are usually +/- as wide as they are long and usually widest in middle or toward base.  NOT [Spikes androgynous, (lateral spikes occasionally pistillate in C. prairea); if heads have indistinguishable spikes, the heads are usually oblong to elongate in shape.]
bulletLower 3 or 4 spike bracts usually scale-like or bristle-like; if lowest is long and leaf-like, then it is shorter than half the culm length or it appears to be an extension of the culm to which inflorescence is attached laterally (as in C. athrostachya); perigynia various.  NOT [Lower 3 or 4 spike bracts long, pale-green and leaf-like; lowest bract 5-15 (20) cm long, usually half to fully as long as culm below inflorescence; perigynia 5 mm long or longer, narrowly lanceolate.]
bulletPerigynium margins flattened as a narrow or wide wing for all or part of perigynium length (wing reduced to raised thickened nerve along body in C. adusta); mature achene narrower than perigynium body; beak present (though may be ill-defined); neither perigynium base nor perigynium wall thickened with spongy tissue.  Section Ovales.  NOT [Perigynium distinctly wingless though margins may be thickened as rounded or raised nerves; mature achene filling width of perigynium body; perigynium base or wall thickened by spongy tissue or cells; beak present or absent.]
bulletSpike bracts usually shorter, or a bit longer than the inflorescence; if much longer then clearly positioned beneath spike and appearing lateral rather than extending culm-like beyond inflorescence.  NOT [Lowest spike bract distinctly longer than the inflorescence and appearing to be an extension of culm with inflorescence attached to one side rather than at tip.]
bulletPerigynia 5.2 mm long or less (occasionally to 6 mm); distance from tip of beak to top of achene 3 mm at most; inflorescence nodding or erect; species not confined to Cypress Hills.  NOT [Perigynia 6-8 mm long (occasionally as short as 5.5 mm); distance from tip of beak to top of achene 3.24.6 mm; inflorescence stiffly erect; Cypress Hills only.]
bulletSpikes distinguishable, or indistinguishable in a compact head; perigynia at most 3 times longer than wide (C. praticola occasionally narrower but then pistillate scales covering perigynia); other features variable.  NOT [Spikes distinguishable; perigynia usually 4 times longer than wide, 3-4 (4.7) mm long and seldom over 1 mm wide; scales distinctly shorter than perigynia; veins absent or faint on both surfaces of perigynia.]
bulletPerigynium body narrower, somewhat contracted or tapering into beak; scale width and perigynium color variable.  NOT [Perigynium body orbicular, abruptly contracted into beak, remaining green until turning tan at maturity; pistillate scales one-third to two-fifths as wide as perigynia.]
bulletScales not resembling wax paper, color various; perigynia not yellow at base.  NOT [Scales scarious-translucent, resembling wax paper, whitish to yellowish with pale (never green) prominent midrib; perigynia yellow at base, faintly nerved.]
bulletPistillate scales, at least those in the middle and upper part of spike, distinctly narrower and/or shorter than the mature perigynia, revealing margins and/or beak.  NOT [Pistillate scales throughout the spike similar in size and shape to the mature perigynia, and more or less concealing them.]
bulletSpikes distinguishable in a compact to elongate inflorescence.  NOT [Spikes indistinguishable in a dense head that is truncate and widest at base, and approximately as wide as it is long.]
bulletLeaves 3-7.5 mm wide; spikes separate to overlapping at base in an elongate head 2-4 cm long; leaf sheaths loose and somewhat winged (flanged) on one or both sides, the wing(s) extending down from junction of sheath and blade.  NOT [Leaves 1-3 mm wide, if to 4.5 mm wide, then spikes densely overlapping to densely bunched in a compact head 1-3 cm long; leaf sheaths tighter and lacking wings below junction of sheath and blade.]
bulletSpikes globose to nearly-globose; proximal perigynia usually spreading to reflexed (at angles of 80 degrees or more from vertical axis); distance from tip of beak to top of achene 1.5-1.8 (2) mm; internode between the 2 lowest spikes 2-6 mm long, internode between the second and third lowest spikes 2-4 mm long (fna).  NOT [Spikes nearly-globose to ovate-oblong; proximal perigynia usually appressed-ascending to somewhat spreading (at angles of 40-75 degrees from vertical axis); distance from tip of beak to top of achene 1.6-2.4 mm; internode between the 2 lowest spikes (4) 5-12 (18) mm long, internode between the second and third lowest spikes 3-11 mm long (fna).]