Usually glabrous, annual herbs with whitish fibrous roots. Leaves linear. Inflorescence capitate, subtended by an involucre of bracts. Involucral bracts ± orbicular to narrowly lanceolate, longer or shorter than the inflorescence. Perianth of 2 whorls, each whorl 2-3-merous. Segments of the outer whorl of male flowers free or basally united, inner whorl forming a tube, with a black gland at the apex of each segment. Segments 4-6, a rudimentary gynoecium sometimes present. Segments of the outer whorl in female flowers free or connate, inner segments free, with an apical black gland, or sometimes the segments lacking. Style absent. Seeds with a striped surface.