Annual herb, 40-60 cm tall, erect, usually with 1-2 main branches; roots long, thin, tuberous. Branches 4-angled, often grooved, ± glabrous, or with trichomes on 2 opposite sides. Petiole ca. 15 mm long; blade ovate to oblong, 3.7-6 x 2.7-3.5 cm, rather thick, glabrous or very sparingly pubescent; margin crenulate, covered with numerous minute cystoliths. Inflorescence axillary, dichasium with sometimes cleistogamous lateral flowers; peduncle ca. 18-34 mm long, glabrous; pedicels 1-6 mm long, glabrous; bracteoles narrowly linear, shorter than or equal to pedicels, sometimes in cleistogamous flowers equal to one half as long as calyx. Calyx lobes 14.5 x 0.5-1 mm at maturity, smaller, 10 x 0.6 mm in cleistogamous flowers, lobes glabrous to sparingly puberulous; corolla of open flowers blue to mauve, darker in throat, tube 10-12 mm long, externally pubescent towards apex, throat slightly oblique to tube, 22-25 mm long, pubescent, lobes 16-17 x 13-15 mm, spreading, corolla of cleistogamous flowers 4-5 mm long, terete, constricted just above base, fugacious, lobes ciliate, not spreading; filaments, ca. 8.5 mm and 4.3 mm long, anthers white, pubescent on their dorsal surface; ovary in open flowers glabrous except for a few glandular trichomes at apex, ovules ca. 13, in 2 rows in each locule, style pale blue, ca. 21 mm long, sparsely pubescent, stigma ca. 1.9 mm long. Capsule cylindric, 17-23.5 x 3 mm, glabrous except for a few glandular trichomes on light-colored, arrow-shaped area near apex, exploding on contact with water; seeds ca. 20-26, each 2-2.5 mm in diam.
Guianas present, Southern America, northern S America present
West Indies and northern S America; 130 collections studied of which 29 from the Guianas (GU: 11; SU: 13; FG: 5).