Annual herbs 10-60 cm tall, glabrous but minutely papillose at the nodes and on the inflorescences, especially when young; stems slender, erect, simple or branched above, 4-ridged. Leaves cauline in remote pairs, the lower often reduced in size, narrowly elliptic to elliptic (to ovate in Madagascar specimens) cuneate at the base, 1-5 cm long, 4-10 mm broad, 3-5 nerved. Flowers borne in slender-branched, terminal and axillary, dichotomous cymes. Calyx of 5 segments, each 3-25-4-75 mm long, 0-9-1-5 mm broad, thin membranous, ovate-lanceolate, joined at the base for 0-5-1 mm, each with a green, veined wing, which is minutely papillose along the margin; calyx, but especially the wings, accrescent, the latter, in fruit, up to 2-5 mm broad. Corolla blue, turning yellow when dry; tube 3-4 mm long, broadly cylindrical or slightly widened at the mouth, the lower portion becoming distended as the ovary enlarges; lobes 2-25-3 mm long, 1-5-2-5 mm broad, suborbicular to obovate or ovate, rounded, erect. Stamens inserted 0-5-0-75 mm (1 mm in the type) below the corolla-sinuses; filaments 0-75-1-25 mm long; anthers 0-75-1-25 mm (1-75 mm in the type) long,
