Gentianaceae, the Gentian Family
Herbs, with opposite or basal, entire, usually simple leaves and regular flowers; sepals, petals, and stamens equal in number, 4-12; ovary superior, 1-celled.
| 1a. Leaves reduced to small scales (1-4 dm. high; flowers small, greenish-yellow, in summer) | Bartonia, Bartonia virginica. |
| 1b. Leaves rounded, floating (flowers white, summer) | Floating Heart, Nymphoides lacunosum. |
| 1c. Leaves compound (2-4 dm. high; flowers white or bluish, early summer) | Buckbean, Menyanthes trifoliata. |
| 1d. Leaves simple, whorled (1-2 m. high; flowers yellowish-white, summer) | American Columbo, Frasera caroliniensis. |
| 1e. Leaves simple, opposite — 2. | |
| 2a. Corolla rotate, with spreading lobes, 2-4 cm. broad, pink (5-8 dm. high; summer) | Rose Pink, Sabbatia angularis. |
| 2b. Corolla bell-shape, each petal with a spur at the base, purplish or white, and not over 1 cm. long (1-4 dm. high; summer) | Spurred Gentian, Halenia deflexa. |
| 2c. Corolla bell-shape, tubular, funnel-form, or salver-form, not spurred — 3. | |
| 3a. Corolla-lobes fringed (flowers bright-blue) (Fringed Gentian) — 4. | |
| 3b. Corolla-lobes entire — 5. | |
| 4a. Leaves lanceolate (2-8 dm. high; autumn) | Fringed Gentian, Gentiana crinita. |
| 4b. Leaves linear (1-4 dm. high; late summer) | Fringed Gentian, Gentiana procera. |
| 5a. Corolla 2 cm. long or a little less — 6. | |
| 5b. Corolla 2.5-5 cm. long (late summer and autumn) (Gentian) — 7. | |
| 6a. Upper leaves linear or narrowly lanceolate (2-4 dm. high; flowers pink-purple, late summer) | Centaury, Centaurium umbellatum. |
| 6b. Upper leaves ovate, with several principal veins (1-5 dm. high; flowers blue, late summer and autumn) | Gentian, Gentiana quinquefolia. |
| 7a. Calyx-lobes rough or ciliate at the margin (flowers blue, or rarely white) — 8. | |
| 7b. Calyx-lobes smooth (2-8 dm. high) — 10. | |
| 8a. Corolla-lobes spreading; leaves narrowly lanceolate, indistinctly veined (2-5 dm. high) | Gentian, Gentiana puberula. |
| 8b. Corolla-lobes erect or incurved; leaves ovate to ovate-lanceolate, with 3-7 principal veins (3-6 dm. high) — 9. | |
| 9a. Calyx-lobes equaling or exceeding the calyx-tube | Gentian, Gentiana saponaria. |
| 9b. Calyx-lobes shorter than the calyx-tube | Gentian, Gentiana andrewsii. |
| 10a. Leaves ovate or ovate-lanceolate, somewhat cordate at base (flowers greenish-white or yellowish-white) | Gentian, Gentiana flavida. |
| 10b. Leaves narrowly lanceolate or nearly linear, not cordate (flowers blue) | Gentian, Gentiana linearis. |