Veterinary Medicine Library

Crown-of-Thorns (Euphorbia milii)

| Description | Distribution | Conditions of poisoning | Control | Toxic principle | Clinical signs | References



A low-growing evergreen shrub with very thorny grooved stems and branches. The stems are purplish brown and are 1-2 feet tall on average, but can reach 3 feet in a warm climate. The thorns are sharp pointed and are 1/2 inch long on avarage. The ovate leaves are 1-3 inches long, few in number, and are found mostly at the growing ends. The cyathia, a type of inflorescence characteristic of the genus Euphorbia, are born in small umbels and have showy, ovate and bright red bracts. The small flowers are produced in clusters of 2-8 at the tips of green flower stem about 1 inch long. Genus Euphorbia includes other commonly available plants such as poinsettia (E. pulcherrima) and snow-on-the-mountain (E. marginata).


A native of Madagascar, crown of thorns is widely grown as a house plant in northern states including Illinois, and as a common garden plant in southern states, especially Florida.

Conditions of poisoning

The poisonous principle is present in all parts of the plant. Euphorbia species generally are highly unpalatable, but animals may eat them due to lack of good forage. Drying does not destroy the toxicity of the plant, and Euphorbia in hay may be slightly more palatable to livestock. Contact with the white, milky sap may cause severe blistering as well as intense pain to open cuts or eyes. Honey made from the flowers of these plants may be toxic.


Light infestations of pastures usually are not a problem since most Euphorbia can be grazed to a limited degree without noticeable reactions. Mowing and reseeding with hardy pasture plants is helpful for heavier infestations of Euphorbia, since most pasture species are annuals; light restocking rates also may help increase the predominance of desirable forage species. Supplemental feeding is suggested in some areas when desirable forage is scarce.

Toxic principle

The poisonous principles have been identified as phorbol esters. Phorbol esters activate protein kinase C. Protein phosphorylation is increased by protein kinase C which may alter multiple enzyme and other protein functions. Effects may result in cytoskeletal damage and tumor promotion.

Clinical signs

Generally horses, cattle, sheep, cats, dogs and humans are affected by Euphorbia and may experience severe irritation of the mouth and gastrointestinal tract, sometimes with hemorrhage and diarrhea. Other general signs include blistering, swelling about the eyes and mouth, excessive salivation and emesis, abdominal pain and weakness. The sap may cause dermatitis. Death is rare. Work horses may suffer severe blisters and loss of hair on the ankles. Approximately 3 kg of E. prostrata and E. marginata when fed to cattle produces severe scours and emaciation.

Other References:

genus Euphorbia in Wikipedia

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