Annual, decumbent or erect, quadrangular, pubescent herb; leaves opposite, rarely whorled, toothed or pinnatifid, more or less pubescent, hoary on the nerves beneath; flowers in terminal, usually many-flowered, corymbose, dense spikes or heads; bracts linear, equal to calyx lobes; calyx campanulate, apparently 4-lobed, sepals-5, 4 oblong, 1-linear, united into tube, setaceous, margins scarious, teeth minute; corolla lilac purple, hyocrateriform or infundibuliform, throat hairy, lobes 5, tube cylindrical, straight or curved, usually villous at the point of stamen insertion, barbate at mouth; stamens-4, didynamous, inserted in the upper half of corolla-tube, anthers ovate; ovary entire or 4-celled, 4-locular; ovule solitary in each locule, style shortly bifid towards apex; fruit schizocarpous of 4-pyrenes, 3-ribbed, smooth, enclosed by the mature calyx; seeds oblong, erect.