Fls perfect; cal of one herbaceous abaxial sep; stamen 1, between the sep and the ovary; ovary compressed; styles 2, very short; pericarp free from the seed, but apparently adherent when dried, cellular-reticulate; seed flat, vertical, acute-margined; embryo annular; branched annuals with small, entire or few-toothed lvs and dense clusters of small sessile fls in the upper axils, forming a leafy terminal spike. 3, w. N. Amer.