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.)

Because of the relatively late recognition of Gentiana austromontana as a distinct species, specimens of this species have been identified both as G. clausa and as G. decora. Gentiana austromontana is distinguished from G. andrewsii, G. clausa, and G. latidens by the combination of puberulent stems and calyx tubes with free portions of the corolla plicae that are about as long as the lobes and about twice as wide, divided into two more or less triangular segments each similar to a true lobe in size and shape. Because of its puberulence, it has been confused with G. decora, which differs in its more open, generally paler corollas with longer lobes and plicae, and usually narrowly linear calyx lobes.

Both Gentiana austromontana and G. decora occur in the higher elevations of eastern Tennessee and western North Carolina, although G. decora tends to occur in shadier habitats. These species are usually distinctly dissimilar, in each case bearing a greater resemblance to other species than to each other, but populations of plants variously intermediate between the two occur relatively frequently, especially in Greene and Unicoi counties, Tennessee. Plants otherwise typical of G. austromontana but with narrowly open corollas have been found in Mount Jefferson State Natural Area, Ashe County, North Carolina, and may be derived from introgression of genetic material from G. decora. Gentiana austromontana also hybridizes occasionally with G. clausa.

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