Annuals to perennial weedy herbs. Stems procumbent to erect, pubescent along one or two opposite sides. Leaves opposite, linear, expanding below into membraneous connate and often ciliolate bases; stipules absent. Flowers tiny, arranged in lax or dense, axillary or terminal cymes; bracts leaf-like. Sepals 5, equal or nearly so. Petals absent. Stamens 1-10 (1-10 fertile). Ovary bi-valved; styles 2, long, filiform., free. Fruit nutlet-like, enclosed by indurate calyx (plus the enlarged wall of the perigynous zone). Seeds smooth.