1	Terminal spike staminate (or androgynous in C. adelostoma).		(2)
+	Terminal spike gynecandrous (or wholly pistillate in C. parryana, C. hallii, and C. idahoa).		(10)
2 (1)	Lateral spikes always present, all spikes of similar length.		(3)
+	Lateral spikes absent, or mostly much shorter than terminal spike as long as terminal in C. parryana (C. hallii and C. idahoa can have single, terminal, staminate spike) [See also the key to unispicate Carex].		(6)
3 (2)	Leaves 3–7 mm wide; perigynia smooth; culms smooth or nearly so.		225 Carex raynoldsii
+	Leaves 1.5–4 mm wide; perigynia papillose; culms scabrous.		(4)
4 (3)	Perigynia distinctly beaked, veinless.		211 Carex stylosa
+	Perigynia beakless or minutely beaked.		(5)
5 (4)	Perigynia brown, obscurely veined; arctic.		212 Carex holostoma
+	Perigynia pale green, veinless; subarctic.		217 Carex adelostoma
6 (2)	Perigynia 3–6.6 × 1.2–3.4 mm; beak veined, 0.5–1 mm.		(7)
+	Perigynia 2–3 × 2–2.5 mm; beak veinless, minute to 0.2 mm.		(8)
7 (6)	Perigynia (2–)3–5 × 1.2–2 mm.		226 Carex serratodens
+	Perigynia (4.7–)5–6.6 × 2.2–3.4 mm.		227 Carex aboriginum
8 (6)	Pistillate scales dark brown to black, mostly exceeding perigynia.		215 Carex idahoa
+	Pistillate scales light to dark brown, shorter than, equaling, or only barely exceeding perigynia.		(9)
9 (8)	Lateral spikes much shorter than terminal spike.		214 Carex hallii
+	Lateral spikes (1 or more) as long as terminal spike.		213 Carex parryana
10 (1)	Lateral spikes sessile or short-pendunculate; spikes, at least proximal, sometimes separate and distinct; distal spikes forming dense terminal cluster.		(11)
+	Lateral spikes pedunculate; spikes contiguous or separate; distal spikes not forming a dense terminal cluster.		(18)
11 (10)	Achenes nearly filling body of perigynia.		(12)
+	Achenes filling proximal 1/2 or less of perigynia.		(14)
12 (11)	Plants with long-creeping rhizomes; perigynia 4–5 mm; beak 0.6–0.8 mm; pistillate scales longer than perigynia; Yukon, Alaska.		209 Carex sabulosa
+	Plants without long-creeping rhizomes; perigynia 2–3.5 mm; beak 0.2–0.4 mm; pistillate scales; North America, Eurasia.		(13)
13 (12)	Perigynia green or golden brown, veinless; pistillate scales with hyaline margins, equaling or shorter than perigynia.		205 Carex norvegica
+	Perigynia dark brown to purple-black, often veined proximally; pistillate scales without hyaline margins, 1/2 as long as perigynia.		206 Carex media
14 (11)	Perigynia ovate or elliptic.		(15)
+	Perigynia obovate.		(16)
15 (14)	Perigynia ovate, abruptly beaked; pistillate scales dark brown to almost black with hyaline margins; beak 0.4–0.5 mm.		223 Carex nova
+	Perigynia elliptic, gradually beaked; pistillate scales blue-black with hyaline margins; beak 0.8–0.1 mm.		224 Carex nelsonii
16 (14)	Pistillate scales as wide as perigynia, usually shorter than or equaling perigynia; distal margins of perigynia papillose, frequently serrulate.		223 Carex nova
+	Pistillate scales narrower than perigynia, usually longer than perigynia; distal margins of perigynia smooth, not serrulate.		(17)
17 (16)	Perigynia dark brown to purple-black; pistillate scales attenuate and mucronate, more than to 2 times as long as perigynia.		221 Carex helleri
+	Perigynia glossy reddish brown; pistillate scales acute, equaling or barely exceeding perigynia.		222 Carex pelocarpa
18 (10)	Proximal lateral spikes spreading or pendent.		(19)
+	Proximal lateral spikes erect, not spreading or pendent.		(24)
19 (18)	Perigynia ovate.		(20)
+	Perigynia broadly elliptic or obovate.		(21)
20 (19)	Leaves basal and cauline; proximal leaves bladeless, reduced to sheaths; pistillate scales conspicuously shorter than perigynia.		208 Carex mertensii
+	Leaves all basal; proximal leaves with blades; pistillate scales equaling or exceeding perigynia.		202 Carex chalciolepis
21 (19)	Perigynia broadly elliptic, papillose.		201 Carex atratiformis
+	Perigynia obovate, smooth.		(22)
22 (21)	Pistillate scales as broad as perigynia.		218 Carex bella
+	Pistillate scales narrower than perigynia.		(23)
23 (22)	Terminal spike with 1/3–2/3 staminate flowers at base; perigynia light green; pistillate scales with midveins lighter colored than bodies.		219 Carex heteroneura
+	Terminal spike with fewer than 1/4 staminate flowers at base; perigynia brown with light colored margins; pistillate scales with midveins same color as bodies.		220 Carex epapillosa
24 (18)	Lateral spikes of varying lengths, mostly shorter than terminal spike (Carex hallii and C. idahoa can have a single, terminal spike).		(25)
+	Lateral spikes of similar length.		(27)
25 (24)	Pistillate dark brown to black, scales exceeding perigynia.		215 Carex idahoa
+	Pistillate scales light to dark brown, shorter than, equaling, or barely exceeding perigynia.		(26)
26 (25)	Lateral spikes much shorter than terminal spike.		214 Carex hallii
+	Lateral spikes (1 or more) as long as terminal spike.		213 Carex parryana
27 (24)	Perigynia ovate, gradually beaked; beak 0.5–1 mm, bidentate, teeth spreading.		(28)
+	Perigynia obovate or broadly elliptic, beakless, minutely beaked, or distinctly, abruptly beaked; beak 0.2–0.5 mm, teeth, when present, not spreading.		(29)
28 (27)	Perigynia (2–)3–5 × 1.2–2 mm.		226 Carex serratodens
+	Perigynia (4.7–)5–6.6 × 2.2–3.4 mm.		227 Carex aboriginum
29 (27)	Pistillate scales ovate or broadly lanceolate, apex blunt.		(30)
+	Pistillate scales lanceolate, apex acute to conspicuously long-mucronate.		(31)
30 (29)	Spikes short-oblong or cylindric, 3–4.5 mm wide; perigynia 2–2.5 mm; beak 0.2–0.25 mm.		207 Carex stevenii
+	Spikes oblong or elongate, 5–6 mm wide; perigynia 2.5–3.5 mm; beak 0.3–0.5 mm.		204 Carex atrosquama
31 (29)	Pistillate scales conspicuously long-mucronate.		(32)
+	Pistillate scales acute or short-mucronate.		(33)
32 (31)	Perigynia brown, smooth; beak longer than 0.2 mm.		210 Carex gmelinii
+	Perigynia gray-green, papillose; beak absent or less than 0.2 mm.		216 Carex buxbaumii
33 (31)	Perigynia gray-green, conspicuously papillose throughout; beak minute, less than 0.2 mm.		217 Carex adelostoma
+	Perigynia straw colored, dark brown, or black, conspicuously papillose along distal margins; beak greater than 0.2 mm.		(34)
34 (33)	Pistillate scales acute, dark brown or black to margins.		200 Carex atrata
+	Pistillate scales acute or short-mucronate, light to dark brown with hyaline margins.		(35)
35 (34)	Perigynia dark brown, almost black; pistillate scales equaling perigynia.		203 Carex albonigra
+	Perigynia straw colored; pistillate scales shorter than perigynia.		228 Carex specuicola