Annual, erect, smooth, slender, glabrous herbs; stem and branches acutely tetragonous; leaves sessile, exstipulate, opposite, linear-oblong to elliptic-lanceolate, gradually narrowed into acuminate apex, entire; flowers in very dense clusters, forming knots in axillary or in loose but very short subsessile cymes, much shorter than the leaves; bracts filiform, shorter than the pedicels; calyx red, campanulate, teeth 3-5, short, acute, broadly triangular; petals 3-5, usually minutes intuded in calyx or absent; stamens 2-8 inserted on calyx tube, filament slender; ovary enclosed in the calyx tube, 4-5 celled, ovules many on axile placenta; style short, stigma capitate; capsules irregularly dehiscent, globose, membranous, red, imperfectly circumcise above the middle; seeds subhemispheric, many, minute, black.