The Manual of the Botany of the Northern United States / Including the District East of the Mississippi and North of North Carolina and Tennessee

by Asa Gray

[+] Style filiform, usually deciduous; anthers oblong to linear, mostly twisting or curving in age.

1. Erythræa. Parts of flower 5 or 4; corolla salver-form; anthers twisting spirally.

2. Sabbatia. Parts of flower 5–12; corolla rotate; anthers recurved or revolute.

3. Eustoma. Parts of flower 5 or 6; corolla campanulate-funnel-form; anthers versatile, straight or recurving; calyx-lobes long-acuminate.

[+][+] Style stout and persistent or none; anthers remaining straight.

4. Gentiana. Corolla funnel-form or bell-shaped, mostly plaited in the sinuses, without spurs or glands. Calyx 4–5-cleft.

5. Frasera. Corolla 4-parted, rotate; a fringed glandular spot on each lobe.

6. Halenia. Corolla 4–5-cleft, campanulate, and 4–5-spurred at the base.

[*][*] Lobes of corolla imbricate in the bud; no appendages.

7. Bartonia. Calyx 4-parted. Corolla deeply 4-cleft, somewhat campanulate.