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.)

The name Gentiana linearis var. lanceolata A. Gray was applied originally to plants referable to G. linearis, although the name G. rubricaulis was cited in synonymy. The name G. linearis var. latifolia was applied originally only to G. rubricaulis, but both of these names were applied subsequently to both that species and relatively wide-leaved specimens of G. linearis. This confusion has been responsible in some cases for the rejection of specific status for G. rubricaulis, and for erroneous reports of G. rubricaulis in New York and Vermont. Reports from Nebraska were based on an old misidentification of G. puberulenta. Reports from Saskatchewan were also based on misidentified specimens. Reports of G. rubricaulis in Maine and New Brunswick are correct, although these populations are disjunct by about 775 km from the easternmost populations in Ontario.

In marked contrast to all other species of Gentiana in eastern and central North America, including G. linearis, the involucral leaves of this species are strongly ascending and somewhat conduplicate as well as being wider, and envelop the proximal portion of the flower cluster.

In the vicinity of Lake Superior, where the ranges of Gentiana rubricaulis and G. linearis overlap, these species maintain their distinctness, with G. rubricaulis occurring in calcareous soils and G. linearis in granitic and similar strongly acid soils (J. S. Pringle 1968). A few hybrids of G. rubricaulis with G. andrewsii, which is likewise a calciphile, are known. These hybrids have been designated G. × grandilacustris J. S. Pringle.

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