Herbs annual, (2–)10–40(–60) cm. Stems erect, simple or branched above base. Leaves: basal sometimes withered by flowering, blades spatulate to obovate, 10–35 × 3–9 mm; cau­line blades oblanceolate to ovate or lanceolate, 20–65 × 3–17 mm. Inflorescences terminal and axillary, dichasial cymes; pedicels 5–75 mm. Flowers (4- or)5-merous, (calyx usually 5-lobed); calyx 7–20 mm, with 1 or 2 lobes distinct nearly to base, these ovate, foliaceous, proximally enveloping the others, with 3 or 4 inner lobes, 1 usually distinct nearly to base, the others variably connate, inner lobes lanceolate to narrowly linear, 6–10 mm; corolla pale violet-blue to pinkish white, white, or pale yellow, tubular to narrowly campanulate, (9–)14–20(–24) mm, lobes spreading, ovate, 4–8 mm, apex acute, with a deeply fringed scale at base of each lobe; ovary sessile.

Flowering mid–late summer. Moist meadows, stream banks, open woods; 1900–3500 m; Ariz., Colo., N.Mex., Utah, Wyo.

In Gentianella heterosepala, one or more often two sepals are separate to the base or nearly so; these are distinctly longer than and at least twice as wide as the others, which they envelop proximally. According to N. H. Holmgren (1984b), plants considered intermed­iate between this taxon and G. amarella subsp. acuta had generally been so interpreted only because of their having unequal calyx lobes. Other aspects of their floral morphology were characteristic of G. amarella subsp. acuta. Following Holmgren, whose observations were supported in studies for the present work, such plants from the Intermountain Region are considered to repre­sent variability within G. amarella subsp. acuta rather than true intergradation. Specimens previously identified as G. heterosepala from sites north to Saskatchewan, Idaho, and Montana are likewise included within G. amarella subsp. acuta, as the variation among the lobes of individual calyces of these plants does not reach the extremes that characterize G. heterosepala. Specific status for G. heterosepala, following G. L. Nesom (1991g), is thus supported, although some hybridization with G. amarella subsp. acuta may occur. These taxa also differ in seed diameter, which is about 1 mm in G. heterosepala and 0.75 mm or less in G. amarella subsp. acuta (J. M. Gillett 1957).