Hymenoxys odorata is a species of flowering plant in the daisy family known by the common names bitter rubberweed and western bitterweed. It is native to the southwestern and south-central United States from southern California to Texas north as far as Kansas and Colorado, as well as northern Mexico (Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Sonora, Tamaulipas). It grows in dry regions.
Hymenoxys odorata is an annual herb producing a branching stem up to 60 centimeters (2 feet) tall. The stems are covered in a foliage of short leaves which are divided into narrow, pointed lobes. Each of the many flower heads contains 50–150 bright yellow disc florets and 8–13 short yellow ray florets.
Hymenoxys odorata is poisonous to livestock; it is mostly a problem of the sheep industry. The toxic compounds are sesquiterpene lactones called hymenovin and hymenoxon. When ingested by sheep the plant produces inflammation of the stomach, renal necrosis, and toxic hepatitis, as well as inhibition of clotting factors. An ill sheep may be bloated, anorexic, weak, drooling, and vomiting. Acute and chronic, cumulative poisoning is often fatal. Sheep tend to avoid the plant because they find it distasteful but they will eat it in the absence of other forage.
- Tropicos, Hymenoxys odorata DC.
- Biota of North America Program 2014 county distribution map
- Calflora taxon report, University of California, Hymenoxys odorata DC., bitter rubberweed, fragrant bitter weed
- SEINet, Southwestern Biodiversity, Arizona chapter
- Flora of North America, Hymenoxys odorata de Candolle 1836. Western bitterweed, bitter rubberweed
- Poisonous Range Plants of Temperate North America Merck Veterinary Manual
- Pfeiffer, F. A.; Calhoun, M. C. (1987). "Effects of environmental, site and phenological factors on hymenoxon content of bitterweed (Hymenoxys odorata)". J Anim Sci. 65: 1553–62.
- Witzel, D. A.; Jones, L. P.; Ivie, G. W. (1977). "Pathology of subacute bitterweed (Hymenoxys odorata) poisoning in sheep". Vet Path. 14 (1): 73–8. doi:10.1177/030098587701400109.
- Steel, E. G.; Witzel, D. A.; Blanks, A. (1976). "Acquired coagulation factor X activity deficiency connected with Hymenoxys odorata DC (Compositae), bitterweed poisoning in sheep". Am J Vet Res. 37 (12): 1383–6. PMID 999065.
- Bitter Rubberweed (Hymenoxys odorata) USDA Poisonous Plants Research
- Jepson Manual Treatment, University of California
- United States Department of Agriculture Plants Profile
- Photo of herbarium specimen collected in Nuevo León in 2000
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