1	Styles distinct		(2)
+	Styles connate [subsect. Rigida]		(14)
2 (1)	Stigmas linear [subsect. Halolinum].		37 Linum trigynum
+	Stigmas capitate [subsect. Linopsis]		(3)
3 (2)	Stipular glands present [ser. Linopsis]		(4)
+	Stipular glands absent		(6)
4 (3)	Proximal leaves in whorls of 4.		8 Linum schiedeanum
+	Proximal leaves opposite or alternate		(5)
5 (4)	Styles 2–3 mm; petals 4–6.5 mm; Florida.		9 Linum arenicola
+	Styles 3–6.5 mm; petals 7–11 mm; New Mexico, Texas.		10 Linum rupestre
6 (3)	False septa incomplete, proximal margins ciliate		(7)
+	False septa nearly complete, proximal margins sparsely or not ciliate [ser. Virginianum (in part)]		(9)
7 (6)	Capsules turbinate, 2–3 mm; anthers 0.5–1 mm; c, e United States [ser. Virginianum (in part)].		13 Linum intercursum
+	Capsules triangular-ovoid to broadly ovoid or ovoid-pyriform, 2.3–4 mm; anthers 1–2.5 mm; w United States [ser. Neomexicana]		(8)
8 (7)	Annuals, 15–60 cm; inflorescences thyrses; styles 1.5–3 mm; capsule apices obtuse.		11 Linum neomexicanum
+	Perennials, 5–30 cm; inflorescences panicles or thyrses; styles 4–7 mm; capsule apices pointed.		12 Linum kingii
9 (6)	Capsules 1.3–2.3 mm, depressed-globose (broader than long) or globose, apices depressed		(10)
+	Capsules 2–3.9 mm, either pyriform to ovoid or subglobose, apices abruptly short-pointed, obtuse, or 5-apiculate		(12)
10 (9)	Margins of inner sepals usually glandular-toothed, rarely entire; mature capsule segments usually persistent on plant.		17 Linum medium
+	Margins of inner sepals eglandular or with a few small sessile glands; mature capsule segments falling freely		(11)
11 (10)	Inflorescences corymbs; pedicels 1–10 mm; carpels flattened or ± concave abaxially.		18 Linum virginianum
+	Inflorescences panicles; pedicels 0–4 mm; carpels convex abaxially.		19 Linum striatum
12 (9)	Leaves mostly opposite; capsules subglobose, apices abruptly short-pointed.		16 Linum westii
+	Leaves: proximal usually opposite, distal alternate, rarely all alternate; capsules pyriform to ovoid, apices obtuse or minutely 5-apiculate		(13)
13 (12)	Margins of inner sepals entire; capsules 3.4–3.9 mm; seeds 2.8–3 mm.		14 Linum macrocarpum
+	Margins of inner sepals glandular-toothed; capsules 2–3.4 mm; seeds 1.6–2.5 mm.		15 Linum floridanum
14 (1)	Capsules dehiscing into 10, 1-seeded segments; sepals persistent [ser. Sulcata]		(15)
+	Capsules dehiscing into 5, 2-seeded segments; sepals deciduous or persistent [ser. Rigida]		(16)
15 (14)	Sepals (3.1–)3.6–5(–7.3) mm, apices acuminate.		20 Linum sulcatum
+	Sepals 2.3–3.7 mm, apices acute.		21 Linum harperi
16 (14)	Sepal margins not glandular-toothed		(17)
+	Sepal margins (some or all) glandular-toothed		(18)
17 (16)	Distal leaves and bracts not ciliate; capsule false septa entirely hyaline, or with cartilaginous portion very narrow, uniform, distal.		22 Linum hudsonioides
+	Distal leaves and bracts sparsely ciliate; capsule false septa with cartilaginous portion conspicuously broader near base.		23 Linum imbricatum
18 (16)	Outer sepals ovate or obovate, margins undulate or crenate, with sessile gland near summit of each crenation.		28 Linum alatum
+	Outer sepals linear, linear-lanceolate, lanceolate, or narrowly ovate, margins glandular-toothed		(19)
19 (18)	False septa incomplete, proximal margins terminating in loose fringe; sepals persistent		(20)
+	False septa complete, proximal margins not terminating in loose fringe; sepals usually deciduous		(21)
20 (19)	Styles connate to within 0.8–3 mm of apex; pedicels (5–)20–30(–60) mm; stipular glands absent.		24 Linum subteres
+	Styles connate to within 0.2 mm of apex; pedicels 2–12 mm; stipular glands usually present.		25 Linum vernale
21 (19)	Plants gray-puberulent throughout or puberulent or glabrescent in proximal 1/3		(22)
+	Plants glabrous, glabrate, scabrous, or puberulent or hirsutulous at base		(23)
22 (21)	Herbs, annual or short-lived perennial, gray-puberulent throughout.		26 Linum puberulum
+	Subshrubs, puberulent or glabrescent in proximal 1/3, otherwise glabrous.		27 Linum allredii
23 (21)	Sepals linear-lanceolate		(24)
+	Sepals lanceolate to narrowly ovate		(25)
24 (23)	Petals obovate; stamens 5–7 mm; styles 4.5–7 mm.		29 Linum aristatum
+	Petals obcordate; stamens 4–5 mm; styles 3–4 mm.		31 Linum lundellii (in part)
25 (23)	Stipular glands usually absent		(26)
+	Stipular glands usually present at least at some nodes		(28)
26 (25)	Styles 2.5–4 mm, petals 6–11 mm.		30 Linum compactum
+	Styles 3–11 mm, petals 10–18 mm		(27)
27 (26)	Petals coppery yellow or orange, red-lined or with short pale to deep brown-red zone at base; styles 5–11 mm; sepal apices sharply acute to acuminate; w, c North America.		34 Linum rigidum (in part)
+	Petals orange-yellow throughout; styles 4–6 mm; sepal apices short-awned; s Florida.		36 Linum carteri (in part)
28 (25)	Styles 6–9.5 mm		(29)
+	Styles 2–6 mm		(30)
29 (28)	Petals with prominent wine-colored band proximal to middle.		33 Linum elongatum
+	Petals reddish below middle.		35 Linum berlandieri
30 (28)	Sepal apices aristate; petals yellow to yellow-orange throughout.		32 Linum australe
+	Sepal apices acute to acuminate or short-awned; petals yellow to orange, sometimes with reddish base		(31)
31 (30)	Sepal apices short-awned; s Florida.		36 Linum carteri (in part)
+	Sepal apices acute to acuminate; c United States		(32)
32 (31)	Stamens 4–5 mm.		31 Linum lundellii (in part)
+	Stamens 6–8 mm.		34 Linum rigidum (in part)