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.)

In addition to the color forms noted in the description, a bicolored form of Gentiana calycosa in southwestern Washington has blue corollas with the center of the distal third of the corolla lobes, including the short-acuminate tip, white.

Gentiana calycosa varies greatly in stature and in the size of its leaves and flowers. Most plants of G. calycosa from the Pacific coastal region, including western Washington and Oregon and most of California, have tubular calyces with well-developed, ovate to elliptic lobes varying in size but usually 3–8 mm. In Canada such plants also prevail east to Alberta; southward, in the United States, they also prevail in Wyoming. From eastern Washington and Oregon to Idaho and parts of Montana, and in Nevada and Utah, the calyces are usually cleft and spathaceous, with the lobes much reduced, less than 3.5 mm, and linear, or vestigial or absent. Extreme forms of such plants have been called subsp. or var. asepala. Because of the sporadic rather than continuous distribution of such forms, the intergradation, especially in the vicinity of Mount Rainier, Washington, and in parts of Montana, where populations may include plants approaching both extremes along with intermediates, and the lack of correlation with other morphological variation, such plants are not distinguished taxonomically in this flora. To some extent their occurrence appears to be correlated with warmer, drier regions, and may be influenced by the habitat.

In most of its range, Gentiana calycosa grows in wet alpine meadows and similar moist habitats, but in the western Cascades it almost always grows in drier, north-facing sites on rocky slopes and cliffs. (T. Harvey, pers. comm.). Plants of G. calycosa in well-drained rocky slopes were distinguished as G. saxicola English (1934), not Grisebach (1838). According to C. S. English (1934), these plants differ from those of wet alpine meadows in having erect rather than decumbent stems; internodes mostly about as long as the leaves rather than distal internodes much longer than the leaves; and spreading rather than erect calyx lobes, which are larger and proportionately wider. According to Harvey, in contrast, the stems of the plants from the drier, rocky sites in the western Cascades are more likely to have decumbent stems. No consistent association of these morphological variations or correlation with geographic distribution was substantiated in the studies for this flora, but further study would be desirable, as molecular phylogenetic studies (A. Favre, pers. comm.) suggest that taxonomic recognition of these ecotypes might be appropriate.

There are records of hybrids of Gentiana calycosa with G. affinis var. affinis and G. newberryi var. newberryi.

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