Flora of North America species comparison

Gentianopsis thermalis occurs near the California state line in Washoe County, Nevada, and should be sought in California. This species is known only from one historical record from Arizona.

The range of Gentianopsis thermalis approaches that of G. virgata subsp. macounii only in Montana. Although occasional plants of G. thermalis have linear leaves similar to those that prevail in G. virgata subsp. macounii, the leaves of G. thermalis are usually elliptic-oblong and often more than 5 mm wide. The basal leaves of G. thermalis are usually larger and more numerous than those of G. virgata subsp. macounii and are more likely to persist until flowering.

The four calyx lobes of Gentianopsis thermalis are nearly equally wide. The keels are narrowly but distinctly winged along the midvein all the way to the apex and are often more or less undulate-crisped distally, with the wing usually sharply defined in dark purple. Some specimens from the southern part of the range have keels that are scarcely papillate-scabridulous distally but are otherwise characteristic of the species. The calyx keels of the other western Gentianopsis taxa are smooth rather than papillate-scabridulous, although the less prominent, usually noncrisped keels of G. detonsa, G. holopetala, and G. macrantha may also be narrowly defined in dark purple. The calyx keels of all subspecies of G. virgata are papillate- or granular-scabridulous proximally rather than on the lobes. As compared with those of other Gentianopsis species in the flora area except for G. detonsa subsp. raupii and G. macrantha, the corolla lobes at least of the larger flowers of G. thermalis are more distinctly divided into an oblong proximal portion and an abruptly expanded distal portion, reminiscent of an old-fashioned keyhole. The style of G. thermalis is slender and one-third to nearly as long as the ovary at anthesis, thus being proportionately much longer than that of any other Gentianopsis taxon in the flora area except G. virgata subsp. victorinii. The gynophore is also proportionately long and slender at anthesis, as long as or longer than the style. The tendency among some Gentianopsis taxa for the margins of the stigmas to be petaloid, more or less recurved and crisped, and erose to shallowly lacerate is especially pronounced in G. thermalis.

Gentianopsis thermalis is sometimes treated as a subspecies or variety of G. detonsa and has been designated simply as Gentiana, Gentianella, or Gentianopsis detonsa in some field guides. Molecular studies support the acceptance of G. thermalis at species rank, indicating that it and G. macrantha may be more closely related to G. crinita and G. virgata than to G. detonsa (B. A. Whitlock, pers. comm.).

Gentianopsis thermalis is the official flower of Yellowstone National Park.

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