1	Plants saprophytic, with little or no chlorophyll; leaves scalelike		2 Cotylanthera
+	Plants autotrophic; leaves green, well developed.		(2)
2 (1)	Plants dioecious; corolla lobed nearly to base		13 Veratrilla
+	Plants with perfect flowers; corolla generally distinctly tubular.		(3)
3 (2)	Fertile stamens 1 or 2 (or 3), with distinctly longer filaments; sterile stamens 2 or 3, anthers nonfunctional, filaments distinctly shorter to nearly absent		5 Canscora
+	Stamens all fertile and without some filaments distinctly longer.		(4)
4 (3)	Corolla with plicae extending between lobes.		(5)
+	Corolla without plicae between lobes.		(8)
5 (4)	Stems twining or trailing.		(6)
+	Stems (at least flowering stems) ascending to erect, neither twining nor trailing (plants may be stoloniferous).		(7)
6 (5)	Calyx tube with 5 vascular bundles; nectaries forming a collarlike disc around gynophore; stamens unequal, recurved		7 Tripterospermum
+	Calyx tube with 10 vascular bundles; nectaries 5, on gynophore; stamens equal, straight		8 Crawfurdia
7 (5)	Filaments broadly and asymmetrically winged below middle, abruptly narrowed apically; seeds broadly winged, discoid		8 Crawfurdia
+	Filaments flattened or narrowly winged, tapering gradually toward apex; seeds variously winged or wingless, not discoid		9 Gentiana
8 (4)	Corolla with 4 distinct spurs		12 Halenia
+	Corolla without spurs.		(9)
9 (8)	Anthers opening by apical pores		1 Exacum
+	Anthers opening by longitudinal slits.		(10)
10 (9)	Anthers helically coiled		4 Centaurium
+	Anthers not coiled.		(11)
11 (10)	Stems twining		6 Pterygocalyx
+	Stems not twining.		(12)
12 (11)	Stamens inserted at or very near sinuses of corolla tube.		(13)
+	Stamens inserted on corolla tube distinctly below sinuses.		(15)
13 (12)	Perennials; basal leaves in a well-developed rosette with blades mostly over 5 cm; stem leaves in 1-3 pairs; capsules distinctly curved, valves with bent or twisted tips		10 Latouchea
+	Annuals; basal leaves not in a rosette or rosette leaves not larger than stem leaves; stem leaves often more than 3 pairs; capsules straight, valves without bent or twisted tips.		(14)
14 (13)	Corolla yellow; leaf blade 1-2.5 × 0.5-0.8 mm; corolla lobes contorted in bud		3 Sebaea
+	Corolla blue or purple; leaf blade over 2 × 1 mm but usually much larger; corolla lobes valvate in bud at least toward base		20 Jaeschkea
15 (12)	Nectaries on gynophore; corolla over 5 cm, 5lobed		11 Megacodon
+	Nectaries on corolla; corolla less than 5 cm or if longer then 4lobed.		(16)
16 (15)	Nectaries surrounded by fringed or tubular appendages.		(17)
+	Nectaries not surrounded by fringes or appendages.		(19)
17 (16)	Nectaries on corolla lobes; stigma elevated above ovary, not decurrent		14 Swertia
+	Nectaries on corolla tube near base; stigma decurrent on ovary.		(18)
18 (17)	Corolla lobe with 2 nectaries each in a conspicuous pit; corolla tissue associated with nectary and pit sometimes basally connate, apically lobulate or lamellate		15 Lomatogonium
+	Corolla lobe with 1 nectary not in a conspicuous pit; corolla tissue associated with nectaries lamellate or galeate appendaged, margin entire or erose		16 Lomatogoniopsis
19 (16)	Flowers 4merous; 2 outer calyx lobes narrower than and basally overlapping 2 inner lobes; discontinuous intracalycular membranes present		17 Gentianopsis
+	Flowers 4 or 5merous; calyx lobes equal or nearly so, not overlapping nor in 2 distinct pairs; intracalycular membranes absent.		(20)
20 (19)	Corolla lobes less than 5 × as long as tube.		(21)
+	Corolla lobes at least 5 × as long as tube.		(22)
21 (20)	Corolla with 1 or 2 nonvascularized fringed scales at base of each lobe		18 Comastoma
+	Corolla either without appendages or with a single vascularized fringed scale at base of each lobe		19 Gentianella
22 (20)	Nectaries on corolla lobes; stigma elevated above ovary, not decurrent		14 Swertia
+	Nectaries on corolla tube near base; stigma decurrent on ovary.		(23)
23 (22)	Corolla lobe with 2 nectaries each in a conspicuous pit; corolla tissue associated with nectary and pit sometimes basally connate, apically lobulate or lamellate		15 Lomatogonium
+	Corolla lobe with 1 nectary not in a conspicuous pit; corolla tissue associated with nectaries lamellate or galeate appendaged, margin entire or erose		16 Lomatogoniopsis