1	Corollas white; rays 0; plants 2–12 cm; Texas (Big Bend area)		(2)
+	Corollas yellow; rays 0, or 3–5, or 6–18; plants (4–)12–75 cm; Arizona, California, Nevada, New Mexico, Texas, or Utah		(3)
2 (1)	Pappi 0 or callous crowns (bristles 0); plants densely scabrous-pubescent		14 Perityle warnockii
+	Pappi usually of 2–3(–5) bristles; plants glabrate, minutely hairy, or scabrous-hispidulous		15 Perityle bisetosa
3 (1)	Rays 3–5 or 6–18		(4)
+	Rays usually 0 (sometimes 1–2, reduced, in P. ambrosiifolia)		(9)
4 (3)	Leaf blades broadly ovate, ovate-deltate, ovate-lanceolate, or ovate-rhombic; disc florets 11–22; Texas		(5)
+	Leaf blades ± cruciform, subdeltate, or subovate, usually 3-partite or lobed, divided, or pinnate; disc florets 30–200; Arizona, Nevada, New Mexico, Utah		(6)
5 (4)	Disc florets 11–13; Hueco Mountains		34 Perityle huecoensis
+	Disc florets 16–22; Edwards Plateau		31 Perityle lindheimeri
6 (4)	Leaf blades usually ± cruciform, sometimes lobed or pinnate; New Mexico		33 Perityle staurophylla (in part)
+	Leaf blades subdeltate, suborbiculate, or subovate, or deeply lobed, 3-foliolate, or 2–3-pinnate; Arizona, Nevada, Utah		(7)
7 (6)	Disc florets 60–80; leaf blades subdeltate, suborbiculate, or subovate, margins serrate or ± lobed; Nevada, Utah		16 Perityle stansburyi
+	Disc florets 75–200; leaf blades 3-foliolate, or 2–3-pinnate; Arizona		(8)
8 (7)	Leaf blades 2–3-pinnate (lobes linear to flat-filiform, scarcely broad- ened distally)		25 Perityle saxicola
+	Leaf blades usually 3-foliolate (lobes much broadened distally)		26 Perityle gilensis
9 (3)	Plants long-hairy, pilose, or villous		(10)
+	Plants glabrous, or hirtellous, hispidulous, or puberulent, or short-hairy, or short-tomentose		(15)
10 (9)	Leaf blades deeply dissected (lobes relatively numerous, irregular)		(11)
+	Leaf blades entire, serrate, or shallow-lobed		(13)
11 (10)	Phyllaries 4–6.4(–8) mm (apices acute); disc corolla throats broadly tubu-lar to subfunnelform; pappus bristles delicate		28 Perityle lemmonii (in part)
+	Phyllaries 6–9 or (5–)7–13 mm (apices usually attenuate, sometimes acute); disc corolla throats narrowly tubular to narrowly funnelform; pappus bristles moderately stout		(12)
12 (11)	Leaf blades 15–30 mm wide; phyllaries 14–20; Arizona		29 Perityle ambrosiifolia
+	Leaf blades 4–15 mm wide; phyllaries 12–15; Texas		30 Perityle dissecta
13 (10)	Leaf margins entire or with 1–3 lobes per side (leaves all alternate)		22 Perityle villosa
+	Leaf margins serrate (leaves opposite or alternate)		(14)
14 (13)	Pappi usually callous crowns (bristles 0); California		21 Perityle inyoensis
+	Pappus usually of single, delicate bristles 1–3 mm; Arizona, New Mexico		28 Perityle lemmonii (in part)
15 (9)	Plants densely short-hairy or short-tomentose		(16)
+	Plants glabrous, or hirtellous, hispidulous, or puberulent		(17)
16 (15)	Leaf margins serrate; plants densely short-hairy; nw Arizona, Nevada, Utah		23 Perityle tenella
+	Leaf margins usually shallow-crenate; plants densely short-tomentose; sw Arizona		27 Perityle ajoensis
17 (15)	Leaf blades 2–8(–15) mm (stems sparsely leafy)		(18)
+	Leaf blades 3–30 mm (stems moderately to densely leafy)		(20)
18 (17)	Pappus bristles usually 1–3(–4), rarely 0; se Utah		19 Perityle specuicola
+	Pappus bristles usually 0, sometimes 1–2; California, s Nevada		(19)
19 (18)	Heads borne singly or (2–3) in loose, corymbiform arrays; peduncles 10–45(–80) mm; leaf blades usually elliptic, lanceolate, lance-ovate, ovate, or suborbiculate (sometimes linear in var. oligophylla)		17 Perityle megalocephala
+	Heads (2–6) in tight, corymbiform arrays; peduncles 1–10 mm; leaf blades linear		18 Perityle intricata
20 (17)	Pappi usually 0, sometimes 1–2 bristles; plants glabrate or puberulent; Texas		32 Perityle angustifolia
+	Pappi usually of 1–3(–6) bristles, sometimes 0; plants glabrous, hirtellous, or short-hairy; Arizona, Nevada		(21)
21 (20)	Leaf blades usually deeply divided (lobes 3, relatively broad to linear, usually secondarily lobed, cleft, or parted, often ± cruciform, sometimes almost entire); sc Arizona		33 Perityle staurophylla (in part)
+	Leaf blades entire, toothed, or lobed; Arizona, Nevada		(22)
22 (21)	Plants 4–12(–15+) cm; petioles 5–30 mm (equal to or longer than blades; leaves usually glabrous); se Arizona		35 Perityle cochisensis
+	Plants 10–30(–45) cm (petioles shorter than blades; leaves hairy); nw Arizona, se Nevada		(23)
23 (22)	Leaf blades usually 3-lobed to ± cruciform; nw Arizona, se Nevada		20 Perityle gracilis
+	Leaf blades elliptic, lanceolate, or ovate, usually entire or 2–6-toothed; nw Arizona		24 Perityle congesta