California butterweed (Senecio aronicoides) is a member of the sunflower family. Native to Northern and Central California as well as Oregon, California butterweed has not established itself beyond these two states. This tall plant that can reach four feet in height prefers a relatively dry habitat and can be found in open woodlands and forests, chaparral and sagebrush scrub. Although considered a perennial, California butterweed sometimes is a biennial.
The single, stout,upright stem of California butterweed rises from a fleshy root. The oval leaves have petioles (stems) and are arranged in a basal circle around the stem. The stem is almost leafless. The few smaller leaves on the stem are more lance-shaped and lack petioles closer to the terminal end. The plant is slightly wooly or cobwebby.
The California butterweed terminal inflorescence is a corymb composed of flowers whose stalks arise from a single point. The lower flower stalks are longer than the upper stalks giving the inflorescence a flat-topped appearance. The bright yellow “pincushion” flowers are composed entirely of disk flowers. Only rarely will one or two ray flowers appear. (The disk flowers can be compared to the yellow center of a daisy while the ray flowers would be the white petals.) A single row of green bracts surround the flower head. The California butterweed fruit is an achene (single dry seed) topped by a pappus of white, bristle-like hairs. The plant has a milky sap.
Also commonly called rayless ragwort or California groundsel, California butterweed may cause minor dermatitis.
These California butterweed plants were growing along Ash Creek (Lassen County CA) downstream from the Lower Campground.