groundsel, any plant of the very large genus Senecio, widely distributed herbs and (in the tropics) shrubs or trees of the family Asteraceae (aster family). Many grow as vines. Most North American species have small, yellow, daisylike flowers; they are especially abundant in the plains region. Some species of the genus are better known as ragworts. The golden ragwort, or squawweed (S. aureus), was used as an emmenagogue and a vulnerary by Native Americans and settlers. Other species have also been used medicinally. A few have been found to be poisonous to livestock, although others are useful for grazing. The common groundsel (S. vulgaris), naturalized from Europe, is one of the species that is sometimes cultivated. The fruits of groundsels usually have a conspicuous white down (pappus), a characteristic shared by Baccharis halmifolia, the groundsel tree, which is a related shrub of the E United States. Groundsel is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.