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 saponaria is believed to be extirpated from the District of Columbia. Reports from west of the range given here have been based mostly on specimens of G. andrewsii × G. puberulenta, occasionally on G. flavida × G. puberulenta or other hybrids. Some reports from the northeastern United States, including all records from Vermont and upstate New York, were based on specimens of G. clausa that antedate the recognition of that species in standard floras. Other reports have been based on misidentified G. linearis.

The name Gentiana puberula Michaux is typified by a specimen of G. saponaria but has generally been misapplied to G. puberulenta.

Plants from the northern parts of the range of Gentiana saponaria tend to have corollas more nearly closed than those from the southern parts of the range, but their corollas are not so firmly closed as those of G. clausa, the corolla lobes are larger, the summits of the plicae are usually more or less visible in herbarium specimens, and the shape of the calyx lobes is distinctively different. Plants of G. saponaria in the southernmost part of its range tend to have somewhat larger and more open corollas, approaching G. catesbaei in these respects, but they differ in their elliptic rather than ovate leaves and calyx lobes mostly shorter than or about as long as the tube rather than longer. Plants from bog and lake-shore habitats in Watauga County, North Carolina, at 1200 m, above the usual altitudinal range of G. saponaria, have attracted interest because of their linear to narrowly elliptic leaves mostly 3–9 mm wide. Their calyx and corolla morphology strongly supports their inclusion in G. saponaria, as does the occurrence of occasional plants with wider leaves in the same populations. Plants with similarly narrow leaves occur elsewhere in the range of G. saponaria and include those that have been identified as G. cherokeensis.

The epithet saponaria refers to a resemblance of the stems and leaves of this species to those of soapwort or bouncing-bet, Saponaria officinalis (Caryophyllaceae). Soaplike substances were not obtained from the gentian, so the invention of “soap gentian” as a common name is not appropriate.

Gentiana saponaria hybridizes with G. andrewsii relatively frequently in the Ohio Valley and occasionally elsewhere. Hybrids with G. catesbaei, G. clausa, G. decora, and G. puberulenta are also known.

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