Flora of North America species comparison

Varieties 2 (2 in the flora).

Gentiana andrewsii is the only species of Gentiana in which the plicae of the corolla are distinctly longer than the lobes.

Gentiana andrewsii has often been reported outside its actual range. Although the epithets of some of the species that have been confused with or considered inseparable from G. andrewsii have priority, the familiar name G. andrewsii is often misapplied, sometimes because it is assumed that any “closed gentian” is G. andrewsii. As G. clausa was not distinguished from G. andrewsii in standard floras prior to 1950, reports from the northeastern United States based on specimens identified before 1950 should be considered doubtful if the specimens have not been reexamined. Old reports from the southern Appalachians are also questionable because G. austromontana was not recognized until 1964. Some reports from the southeastern and south-central United States and along the Atlantic seaboard have been based on specimens of G. saponaria. True G. andrewsii is distinguishable as the only Gentiana species in which the corolla plicae distinctly exceed the minute lobes. The fringed tip of the completely closed corolla, at first white, soon turning reddish brown, is an excellent field mark for distinguishing G. andrewsii from G. clausa. In G. clausa, the summit of the intact corolla appears completely blue (in the typical color form), and the plicae are concealed. Gentiana andrewsii grows in calcareous soils and G. clausa in noncalcareous soils.

Because of this ecological separation, there are only a few records of hybridization between Gentiana andrewsii and G. clausa. In the tall-grass prairies, G. andrewsii hybridizes with G. flavida, producing G. × pallidocyanea J. S. Pringle, and with G. puberulenta, producing G. × billingtonii Farwell (as species). Northward, it occasionally hybridizes with G. rubricaulis, producing G. × grandilacustris J. S. Pringle, and in the southeastern part of its range it hybridizes with G. saponaria.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Gentiana catesbaei is believed to be extirpated from New Jersey and Pennsylvania. Specimens from Alabama have been reidentified as G. saponaria as all such specimens seen in studies for this flora had the elliptic leaves and short calyx lobes typical of G. saponaria rather than the ovate leaves and much longer calyx lobes that characterize G. catesbaei.

From the more widely distributed Gentiana saponaria, G. catesbaei differs most conspicuously in its ovate rather than elliptic leaves, widest proximal to rather than near mid-length; calyx lobes widest near mid-length and usually 1.5–3 times as long as the tube; and generally with spreading rather than incurved corolla lobes.

Gentiana catesbaei is almost entirely restricted to the Atlantic coastal plain, where it displaces the closely related G. saponaria south of northeastern North Carolina. In the northern part of its range, where the ranges of these species overlap, they generally remain distinct, although a few plants apparently of hybrid origin have been found. A hybrid with the much less similar G. villosa is also known.

(Discussion copyrighted by Flora of North America; reprinted with permission.)