Ovary narrowly ellipsoid, unilocular; ovules numerous; style oblong-cylindric; stigma bilobed.
Filaments included in the corolla tube or exserted; anthers narrowly ellipsoid, not twisted.
Calyx tube cylindric, with 4 ribs and 8 delicate veins, papyraceous; lobes 1-nerved.
Leaves ovate to elliptic or obovate, linear at the apex of the branches, entire.
Flowers 4-merous, axillary, solitary or 2–3-nate.
Stems erect, slender, often branched, 4-angled.
Corolla tube cylindric, with 4-lobes.
Capsule narrowly-cylindric, bivalved.
Annual herbs.