This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Mostly perennial herbs with opposite entire leaves, and large sessile or short-stalked flowers in terminal and axillary clusters, or sometimes solitary, usually 2-bracted under the calyx. Calyx mostly 5-lobed, with an interior membrane. Corolla mostly 5-lobed, clavate to funnelform, with thin lobed or toothed plaits in the sinuses, but without glands. Stamens as many as the corolla-lobes, the anthers cohering in a ring or separate. Ovary 1-celled; ovules very numerous; style short; capsule stipitate. [Greek, rough garland.]
About 75 species, natives of the north temperate zone. Besides the following, several others occur in western North America. Type species: Gentiana asclepiadea L. Margins of leaves and calyx-lobes scabrous or ciliate; seeds winged. Anthers separate, or merely connivent.
Stems usually clustered; calyx-lobes unequal; corolla narrowly funnelform 1. D. afflnis.
Stems mostly solitary; calyx-lobes equal; corolla campanulate-funnelform.
Anthers cohering in a ring or short tube.
Corolla-lobes distinct, longer than or equalling the plaits.
Flowers 1-4; corolla campanulate-funnelform, its lobes 2-3 times as long as the plaits.
3. D. parvifolia.
Flowers several or numerous; corolla club-shaped, its lobes not much longer than the plaits.
4. D. Saponaria.
Corolla-lobes none or minute, the plaits very broad.
Margins of leaves and calyx-lobes smooth or nearly so.
Flowers clustered, sessile, 2-bracteolate under the calyx.
Corolla-lobes ovate, twice as long as the plaits; leaves broad, acuminate; seeds winged.
Corolla-lobes rounded, little longer than the plaits; leaves narrow; seeds winged.
7. D. linearis.
Corolla-lobes ovate, acute, much longer than the broad plaits; leaves broad; seeds winged.
8. D. Grayi.
Corolla-lobes triangular-lanceolate; leaves obovate; seeds wingless.
9. D. vulosa.
Flowers solitary, peduncled, not bracteolate; leaves linear.
10. D. Porphyrio.
Perennial; stems clustered from deep roots, minutely puberulent, simple, 6'-18' high. Leaves linear-oblong to lanceolate-oblong, obtuse or acutish, rounded or narrowed at the base, firm, roughish-margined, indistinctly nerved, 1/2'-1 1/2' long, the floral smaller; flowers few, numerous, or rarely solitary, 5-parted, sessile and solitary or clustered in the axils of the upper leaves, about 1' high, not bracted under the calyx; calyx-lobes linear or subulate, unequal, the longer about equalling the tube, the smaller sometimes minute; corolla narrowly funnelform, blue, its lobes ovate, acute or mu-cronate, entire, spreading, with laciniate appendages in the sinuses; anthers separate; seeds broadly winged.
In moist soil, Minnesota to British Columbia, south in the Rocky Mountains to New Mexico. Aug.-Oct.