1	Calyx 2lobed, enveloping corolla tube		1 Comastoma disepalum
+	Calyx 4 or 5lobed, not enveloping corolla tube.		(2)
2 (1)	Perennials.		(3)
+	Annuals or biennials.		(4)
3 (2)	Leaves mostly restricted to near base of stem; stem leaves few pairs; corolla 1.4-2.5 cm, lobes each bearing 2 scales		2 Comastoma cyananthiflorum
+	Basal leaves absent or poorly developed; stem leaves 4-7 pairs; corolla 0.6-1.3 cm, lobes each bearing 1 scale		3 Comastoma stellariifolium
4 (2)	Corolla salverform.		(5)
+	Corolla tubular.		(7)
5 (4)	Calyx ca. 1/2 as long as corolla, lobes falcate, apex acuminate; stem leaf blades 3-4(-6) mm wide		6 Comastoma falcatum
+	Calyx 1/4-1/3 as long as corolla, lobes erect, apex acute to obtuse; stem leaf blades 5-13 mm wide.		(6)
6 (5)	Stem leaf blades oblong to broadly ovate; calyx lobes ovate-lanceolate to ovate; filaments pilose at base		4 Comastoma traillianum
+	Stem leaf blades lanceolate to elliptic; calyx lobes linear-lanceolate; filaments glabrous		5 Comastoma muliense
7 (4)	Stem leaf blade bases obtuse to rounded, subamplexicaul; corolla lobes shorter than tube, suberect		7 Comastoma pulmonarium
+	Stem leaf blade bases narrowed or cuneate (rounded and abruptly contracted in C. henryi), not amplexicaul; corolla lobes equaling tube, spreading (erect in C. henryi).		(8)
8 (7)	Stem leaves petiolate; leaf blades widest above middle; calyx lobes oblong-spatulate to narrowly elliptic		8 Comastoma henryi
+	Stem leaves sessile; leaf blades oblong or widest at or below middle; calyx lobes lanceolate to ovate.		(9)
9 (8)	Corolla dark blue to blue-purple with dark blue veins and pale yellow base		11 Comastoma pedunculatum
+	Corolla uniformly blue or pale blue.		(10)
10 (9)	Calyx lobes acuminate, margin undulate rugose and revolute		9 Comastoma polycladum
+	Calyx lobes apiculate, margin flat and smooth		10 Comastoma tenellum