Parthenium argentatum, commonly known as the guayule (/ɡwaɪˈuːliː/ or /waɪˈuːleɪ/, as in Spanish), is a flowering shrub in the aster family, Asteraceae, that is native to the southwestern United States and northern Mexico. It was originally discovered by J.M. Bigelow in 1852 and was first described by Asa Gray. It can be found in the US states of New Mexico and Texas and the Mexican states of Zacatecas, Coahuila, Chihuahua, San Luis Potosí, Nuevo Leon, and Tamaulipas. The plant can be used as an alternate source of latex that is also hypoallergenic, unlike the normal Hevea rubber. In pre-Columbian times, the guayule was a secondary source of latex for rubber, the principal source being the Castilla elastica tree. The name "guayule" derives from the Nahuatl word ulli/olli, "rubber".