Common Name
Colorado Rubber Weed, Pingue, Bitterweed
Botanic Name
Hymenoxys richardsonii (hook.) Cockerell Hymenoxys odorata
Plant Family
Asteraceae (compositae)
Dry plains and foothills of the Rocky Mountains.
Animals Affected
Sheep, occasionally cattle.
colorado rubberweed
Toxic Principle
Sesquiterpene lactones appear to inactivate sulfhydryl groups of cellular enzymes. These bitter tasting compounds are present in all parts of the plant even when dry. As little as 0.5 - 1.5% body weight of green plant is toxic.
A upward branching, perennial 10-18 inches in height, arising from a clustered woody stem covered with old leaf bases. Leaves are clustered around the stem base. Multiple yellow flower heads with up to 12 ray florets. Similar species include H. odoata.
Animals that are compelled to eat bitterweeds tend to salivate. cough and vomit rumen contents. Rumen stasis and bloat are common chronic poisoning results in weak, debilitated animals which eventally become recumbent and die. Inhalation pneumonia may cause secondary vomiting.
Muscle weakness, ataxia
Remove animals from the source of the bitterweed and provide nutritious food and water.
Post-mortem examinations have found changes in the lung, heart, and kidney tissues.
Special Notes
Poisoning is infrequent when other forages are available. 1) Witzel DA, Jones LP, Ivie GW. Pathology of subacute bitterweed (Hymenoxys odorata) poisoning in sheep. Vet Pathol. 1977 Jan;14(1):73-8. doi: 10.1177/030098587701400109. PMID: 850997.
colorado rubberweed (Hymenoxys richardsonii)
colorado rubberweed