Sphenosciadium is a monotypic genus of flowering plants in the carrot family containing the single species Sphenosciadium capitellatum, which is known by the common names woollyhead parsnip, ranger's buttons, button parsley, and swamp white heads. The plant is native to western North America from Idaho through Nevada, Oregon, and California into Baja California. It grows in moist habitat types, such as creeksides and meadows. It is included in Toxic Plants of North America (Burrows & Tyrl, 2001). Ranger's buttons plants are quite similar to the other large Umbelliferae that share similar habitats: Sierra angelica and cow parsnip, but each has a very differently shaped leaf, and the other two have umbellets with quite distinct flowers, in contrast to the tight balls on ranger's buttons.