Annual herbs, sometimes fruticose. Leaves opposite, petiolate. Inflorescence of terminal spikes; bract persistent; bracteoles located on outer side of reflexed flower, becoming indurated with spinose apex. Flowers sessile, becoming reflexed early in development; tepals 5, stiff, persistent; stamens 5, separated by 5 fimbriate pseudostaminodia, filaments and pseudostaminodia joined below in a cup, anthers dorsifixed; style filiform, stigma glandular. Fruit an indehiscent, thin-walled utricle, remaining inside persistent tepals and bracteoles; seed 1, more or less cylindrical, testa thin, membranous, pale brown, embryo closely encircling solid perisperm.