Garden Alphabet: Oleander (Nerium) – A Gardener's Notebook

Oleander (Nerium)

Oleander is an extremely common landscape plant around here and, as familiarity breeds contempt, I haven’t thought much about it. In most yards it grows huge and out of control, used only as screening from the street. It does flower nice and, when kept in check, it can be a nice — if bland — addition as a hedge or divider in the garden. Many people don’t realize how poisonous oleander can be, but I haven’t heard of any recent issues with that in our area.

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Nerium oleander /ˈnɪəriəm ˈoʊliː.ændər/^[3] is an evergreen shrub or small tree in the dogbane family Apocynaceae, toxic in all its parts. It is the only species currently classified in the genus Nerium. It is most commonly known asoleander, from its superficial resemblance to the unrelated olive Olea.^{[Note 1]} It is so widely cultivated that no precise region of origin has been identified, though southwest Asia has been suggested. The ancient city of Volubilisin Morocco may have taken its name from the Berber name oualilt for the flower.^[4] Oleander is one of the most poisonous of commonly grown garden plants.

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Nerium oleander has historically been considered a poisonous plant because some of its compounds may exhibit toxicity, especially to animals, when consumed in high amounts. Among these compounds are oleandrin andoleandrigenin, known as cardiac glycosides, which are known to have a narrow therapeutic index and can be toxic when ingested.

Toxicity studies of animals administered oleander extract concluded that rodents and birds were observed to be relatively insensitive to oleander cardiac glycosides.^[12] Other mammals, however, such as dogs and humans, are relatively sensitive to the effects of cardiac glycosides and the clinical manifestations of “glycoside intoxication”.^[12]^[13]^[14]

However, despite the common “poisonous” designation of this plant, very few toxic events in humans have been reported. According to the Toxic Exposure Surveillance System, in 2002, 847 human exposures to oleander were reported to poison centers in the United States.^[15] Despite this exposure level, from 1985 through 2005, only three deaths were reported. One cited death was apparently due to the ingestion of oleander leaves by a diabetic man.^[16] His blood indicated a total blood concentration of cardiac glycosides of about 20 μg/l, which is well above the reported fatal level. Another study reported on the death of a woman who self-administered “an undefined oleander extract” both orally and rectally and her oleandrin tissue levels were 10 to 39 μg/g, which were in the high range of reported levels at autopsy.^[17] And finally, one study reported the death of a woman who ingested oleander ‘tea’.^[18] Few other details were provided.

In contrast to consumption of these undefined oleander-derived materials, no toxicity or deaths were reported from topical administration or contact with N. oleander or specific products derived from them. In reviewing oleander toxicity, Lanford and Boor^[19] concluded that, except for children who might be at greater risk, “the human mortality associated with oleander ingestion is generally very low, even in cases of moderate intentional consumption (suicide attempts)”.^[19]

Toxicity studies conducted in dogs and rodents administered oleander extracts by intramuscular injection indicated that, on an equivalent weight basis, doses of an oleander extract with glycosides 10 times those likely to be administered therapeutically to humans are still safe and without any “severe toxicity observed”.^[20] — Wikipedia