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September–November 2023

Beautiful flowers, lovely perfume, and deadly!

Most Australians and visitors from overseas fear an encounter with one of this country’s venomous snakes or spiders. Fortunately, bite victims treated promptly with anti-venenes usually recover completely. Little do many people realise that, in certain parts of the country, there are plants that are poisonous by ingestion and sometimes simply by touch, for which there are no lifesaving remedies.

In the September–November 2021 issue (p. 35), I wrote about indospicine found in plants of the genus Indigofera, which caused the death of more than 40 dogs in Victoria after they were fed raw meat from horses that had grazed Indigofera linnaei in the Northern Territory. This year, east coast newspapers informed readers in May (Sydney Morning Herald, 9 May; The Age, 10 May) of the death of two previously healthy, well-maintained horses, in Lismore, New South Wales, which allegedly had ingested a common weed, Cestrum nocturnum, belonging to the family Solanaceae (which includes potatoes, tomatoes and eggplants). A third (larger) horse survived.

C. nocturnum has numerous common names – lady of the night, night-blooming jasmine, night-blooming jessamine, night-scented jessamine, night-scented cestrum and poisonberry – derived from observations that the plant flowers open at night, have a particularly alluring perfume and are poisonous. The plant originated in the West Indies but has spread widely in subtropical areas. It is very intrusive and, following floods in New South Wales, has dominated native plants in some parts.

C. nocturnum grows as an evergreen shrub to about four metres. Several related species are also known in Australia: C. parqui (green centrum), C. elegans (red cestrum) and C. auriculatum (orange centrum). All originated in or around South America and were brought to Australia as garden ornamentals. Each has different coloured flowers and berries. Generally, they are described as toxic to mammals.

In Lismore, a local veterinarian inspected the property where the horses were kept and found it was infested with C. nocturnum, with obvious signs that parts of the plants had recently been eaten. He commented that this was the second case he has seen in horses, but other cases have been seen in sheep, goats and cattle. He speculated that C. nocturnum may also be causing the death of native animals, including wallabies.

C. nocturnum and C. parqui can be differentiated by the size, shape and colour of their berries. C. nocturnum has large white berries, whereas mature berries of C. parqui are small and black. Because of the disease risk of carrying out an autopsy on a horse, a blood sample was taken from a third horse that had survived and the liver enzymes were examined. They showed a toxicity profile matching both Cestrum species. Thus, identification of the Cestrum species relied on visual examination of the remaining uneaten parts of the plants; because the liver enzyme profile of the surviving horse was consistent with both C. nocturnum and C. parqui ingestion, the species identification was not definitive.

A search of the literature found that the composition of Cestrum species, and in particular the toxic principles, have not been investigated systematically and reported. Often the plants are simply described as toxic. The New South Wales Department of Primary Industries (NSW DPI WeedWise) has issued information on several Cestrum species, including identification and poisoning. It can be browsed by common name or scientific name.

C. nocturnum – all parts of the plant are poisonous to human beings and livestock. The strong fragrance released from the flowers at night can cause breathing difficulties and irritation of the nose and throat. It can also cause intense headaches, nausea and dizziness.

C. parqui – highly poisonous to cattle and can kill animals and human beings. The plant contains carboxyparquin, a kaurene glycoside that causes severe liver and brain damage. Avoid touching the plant with bare skin.

Since all Cestrum species belong to the family Solanaceae, they would contain solanine, a glycoalkaloid, but seemingly not in sufficient quantities to be toxic. It has been reported that some Cestrum species contain chlorogenic acid, which is abundant in coffee and is therefore unlikely to be the toxic principle.

It seems to me there is an opportunity here for natural products chemists to investigate and clarify the chemistry of these attractive but poisonous plants, now becoming widespread in New South Wales.

Peter G. Lehman FRACI CChem joined RACI as a student member in 1963, subsequently pursuing a career in academia and industry, the latter in Australia and the US. In his retirement, he has been writing occasionally for Chemistry in Australia.

Asit K. Ghosh, Public domain via Wikimedia Commons

The greenish-white flowers of Cestrum nocturnum.

Macleay Grass Man, Public domain via Wikimedia Commons

The yellow flowers and leaves of Cestrum parqui.

... the composition of Cestrum species, and in particular the toxic principles, have not been investigated systematically and reported. Often the plants are simply described as toxic.

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