A smooth, leafy perennial with a much-branched top. Flowers: when growing on poor ground, only a few, but in rich soils plants may spread as wide as they are tall with a large inflorescence. The floral cups have 5 white false petals surrounding tiny yellow male flowers and a single female flower (this arrangement, called a cyathium, is typical of flowers in the spurge family). Blooms May–October. Leaves alternate on lower stems, sessile, narrowing toward base, ovate, with smooth edges. Leaves at the branching points are in whorls. Leaves in inflorescence are opposite. Leaves and stems are usually hairless but some plants have hairs. The sap is milky and can be skin-irritating.