Annual herb 7-30 cm high. Stem erect simple or branched, quadrangular, hirsute. Leaves linear to narrowly lanceolate, 4-20 x 1-4 mm, opposite, acute, entire sessile, hairy. Inflorescence spike or axillary solitary. Flowers bisexual, zygomorphic, sessile, alternate, opposite, or subopposite. Bracts linear 6-18 x 0.5-1.5 mm. Calyx 15-ribbed, 5-lobed, tube 3-5 mm long, lobes 2-4 mm long, lanceolate, acute, hairy. Corolla white, tube 6-15 mm long, lobes 3-6 x 3-4 mm; stamens 4, didynamous, inserted on corolla tube, anthers monothecous. Ovary subglobose, 2-3 x 1-2 mm. Styles 4-7 mm long. Stigma clavate. Capsule ovoid, 4-6 x 2-3 mm. Seeds brown minute.