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.)

Plants of Gentiana sceptrum with ascending, narrowly lanceolate leaves conspicuously exceeded by the distal internodes have been called G. menziesii. Plants with spreading, elliptic to ovate, more closely spaced leaves have been called G. sceptrum var. cascadensis, although that variant might more appropriately be considered nomenclaturally typical. Studies for this flora have indicated that the extremes are connected by many intermediates, and that little correlation exists between leaf shape and geographic distribution, or between leaf shape and the other traits by which the segregates have been characterized, such as stature, erectness of stems, or numbers and sizes of flowers. Even within a relatively limited area, such as Vancouver Island, British Columbia, or Humboldt County, California, plants can be found with leaves ranging from narrowly lanceolate to widely elliptic.

Small plants with strongly decumbent stems, found at a few localities at or near the coast in California and southern Oregon, have been called Gentiana sceptrum var. humilis. Spathaceous calyces occasionally occur in these plants. Such plants are not recognized taxonomically here because larger plants approaching typical G. sceptrum have been found at the same localities or nearby, but they should be given further study.

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