Meadow closed or bottle gentian, gentiane close

Herbs perennial, 2–8 dm, glabrous. Stems 1–10, terminal from caudex, erect or decum­bent. Leaves cauline, ± evenly spaced; blade ovate, 3–15 cm × 10–45 mm, apex acuminate. Inflo­rescences 1–20-flowered heads, sometimes with addi­tional flowers at 1–3 nodes, rarely on short branches. Flowers: calyx 8–22 mm, lobes spreading nearly horizontally, widely obovate or elliptic to orbiculate, 2–6(–10) mm, margins ciliate; corolla blue or occasionally violet or white, tubular, completely closed, 23–40 mm, lobes incurved, ovate-triangular to semicircular, 0.7–2 mm, free portions of plicae ± as long and as wide as lobes, oblong, deeply and unequally bifid, summit erose; anthers connate. Seeds winged. 2n = 26.

Flowering late summer–fall. Moist, open woods, stream banks, roadsides, acid soils; 0–800 m; Que.; Conn., D.C., Maine, Md., Mass., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Tenn., Vt., Va., W.Va., restricted to higher elevations southward.

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.