Flora of North America species comparison

The corollas of Gentiana andrewsii, G. austromontana, and G. clausa all remain completely and tightly closed but are pollinated by bumblebees, which force open the corollas. The fresh corollas of G. clausa are rounded at the summit, with the plicae concealed by the true lobes. In contrast, the fresh corollas of G. andrewsii and G. austromontana are more acute, with the plicae forming much or all of the visible summit. The corolla lobes of G. clausa are about as long and as wide as the free portions of the plicae, whereas those of G. andrewsii and G. austromontana are distinctly narrower than the plicae. Also, in contrast to those of other species of Gentiana in the flora area except for G. flavida and G. latidens, the calyx lobes of G. clausa when fresh spread almost horizontally rather than being nearly erect.

Reports of Gentiana clausa from Indiana to Missouri and elsewhere west of the range given here have been based on specimens of G. andrewsii var. dakotica, second- or later-generation plants derived from G. andrewsii × G. puberulenta, or other hybrids and introgressants. In these plants, in contrast to G. clausa, the sepals are lanceolate and nearly erect, and the lobes of the intact corolla do not entirely conceal the plicae.

Gentiana clausa is largely isolated ecologically and geographically, but a few hybrids with G. andrewsii, G. austromontana, G. decora, and G. saponaria are known.

(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.)