Oncosiphon suffruticosum (Linnaeus) Källersjö [Matricaria suffruticosa (Linnaeus) Druce] was collected on ballast at Portland, Oregon, in 1902. It differs from O. piluliferum by smaller (3–5 mm diam.) heads clustered in dense, ± flat-topped, corymbiform arrays. Both O. piluliferum and O. suffruticosum are common weeds in their native southern Africa and in Australia. Both have the potential to become serious pests in western North America. They are unpalatable to livestock and tend to dominate infested pasturelands. When consumed by animals, they taint the flavor of milk and meat.