About Hymenoxys odorata DC.
Hymenoxys odorata DC. is a species of flowering plant in the daisy family, with common names bitter rubberweed and western bitterweed. It is native to the southwestern and south-central United States, ranging from southern California to Texas and north to Kansas and Colorado. It also grows in northern Mexico, specifically in the states of Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Sonora, and Tamaulipas. This species grows in dry regions. It is an annual herb that produces a branching stem growing up to 60 centimeters, or 2 feet, tall. Stems are covered with short leaves that are divided into narrow, pointed lobes. The plant produces many flower heads, each holding 50 to 150 bright yellow disc florets and 8 to 13 short yellow ray florets. Hymenoxys odorata is poisonous to livestock, and it is primarily a problem for the sheep industry. The toxic compounds in the plant are sesquiterpene lactones called hymenovin and hymenoxon. When sheep ingest this plant, it causes stomach inflammation, renal necrosis, toxic hepatitis, and inhibition of clotting factors. Affected sheep may develop bloating, anorexia, weakness, drooling, and vomiting. Both acute and chronic cumulative poisoning from this plant is often fatal. Sheep generally avoid Hymenoxys odorata because it is distasteful to them, but they will eat it when no other forage is available.
