Toxicity of Rhododendron
“Potentially toxic chemicals, particularly ‘free’ phenols, and diterpenes, occur in significant quantities in the tissues of plants of Rhododendron species. Diterpenes, known as grayanotoxins, occur in the leaves, flowers and nectar of Rhododendrons. These differ from species to species. Not all species produce them, although Rhododendron ponticum does.
These toxins make Rhododendron unpalatable to most herbivores. Phenols are most concentrated in the young tissues, such as young emergent leaves and buds. This provides a primary defense against herbivores, before the tissues have acquired the added deterrent of physical toughness found in older tissues. Young emergent leaf buds have the additional protection of a sticky exudate which also contains phenols. This physically discourages small invertebrates from eating the buds, because they get stuck in the exudate. Its poisonous nature must act as a further discouragement.
Grazing animals are discouraged from eating Rhododendron foliage because of its toughness and unpalatability. The unpalatability is learned and cases of poisoning may result in animals such as sheep and cattle if they ingest sufficient quantities because of extreme hunger or inexperience. The general toxicity of Rhododendron to herbivores means that it cannot generally be controlled by grazing.
Cases of human poisoning are also known. Most are caused by the consumption of honey produced from Rhododendron flowers. This is known as ‘Mad Honey Disease’, or ‘Honey Intoxication’. Cases of this have been recorded from as far back as 400 BC. It results in relatively short-lived intestinal and cardiac problems and is rarely fatal. The severity of symptoms depends on the amount of contaminated honey consumed. It is worth thinking carefully about the siting of bee hives if Rhododendron is a prominent feature of the area.”
From the French Wikipedia
“According to some sources , honey from the flowers of some Asian rhododendrons cause intestinal problems. Indeed, in the plant leaves contain a glucoside strongly emetic. And Xenophon (430-355 BC) described in the Anabasis bizarre behavior of Greek soldiers, Ten Thousand , who scooped the honey of a village surrounded by rhododendrons. All who ate lost reason, vomited, had diarrhea and lost their forces. Those who had eaten were just little drunk. Nobody died, however: after twenty-four hours, the Greeks found themselves the right, and four days later they stood up again.
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Four centuries later, the same thing happened to the armies of Pompey : Pliny the Elder reports that troops were victims of a honey that crazy.
In the eighteenth century, a French botanist, Pitton de Tournefort , reports this feature .
The question was Rhododendron ponticum . Later, it was recognized that the honey from this azalea effects were slightly hallucinogenic and laxative . The Rhododendron ponticum cause digestive disorders contains the andromédotoxine (diterpene alcohol), the Alpine rhododendron (Rhododendron ferrugineum) arbutin, the aricoline and rhodoxanthin. Both rhododendrons are considered moderately toxic plants that cause vomiting, digestive problems, nerve disorders, respiratory and cardiovascular.”
From ‘The Delphic Bee: Bees and Toxic Honeys as Pointers to Psychoactive and Other Medicinal Plants‘ by Johathan Ott which appeared in Economic Botany 52(3):260-266, 1998 we learn the following:
Xenophon’s 4th century B.C. Anabasis (IV, VII, 20) described psychoactive honey-poisoning during the ‘Retreat of the Ten Thousand’ in the ill-starred expedition of Cyrus. Countless soldiers in the Greek army, encamped near Trebizonde in Asia Minor, ate liberally of honey found there, “lost their senses and vomited,” and “resembled drunken persons.” Pliny (XXI, XLV) described madness-inducing honey from this area as meli mcenomenon (‘mad honey’), and also mentioned (XXI, XLVI) a medicinal honey from Crete, miraculum mellis or ‘wondrous honey’ (Halliday 1922; Ransome 1937). The 6th-8th century B.C. Homeric Hymn to Hermes referred to melissai or bee-oracles from Delphi’s Mt. Parnassos, who could prophesy only after ingesting melichloron or ‘green honey’, perhaps a reference to Pliny’s ‘mad honey’. It was conjectured that these bee-oracles were the Pythia, hence psychotropic honey could have been a catalyst for the mantic utterances of the Delphic Bees (Mayor 1995). It is thought the source of meli menomenon was Rhododendron ponticum L., which contains toxic glucosides called andromedotoxins or grayanotoxins (Krause 1926; Plugge 1891; Wood, et al. 1954), found in other species of Ericacee, notably Kalmia latifolia L., another plant whose honey has provoked poisonings (Howes 1949; Jones 1947). Grayanotoxins occur in North American toxic honeys, presumably from K. latifolia (Scott, Coldwell, and Wiberg 1971). Frequent honey poisonings in Japan (Kohanawa 1957; Tokuda and Sumita 1925) were traced to ericaceous Tripetaleia paniculata Sieb. et Zucc., and grayanotoxins were found in these honeys (Tsuchiya et al. 1977). Another toxic glucoside, ericolin, is known from ericaceous Ledum palustre L., and from honeys derived from this plant, which caused human poisonings (Kozlova 1957;Palmer-Jones 1965). Both L. palustre and L. hypoleucum Kam. are used as shamanic inebriants by Tungusic tribes of Siberia (Brekhman and Sam 1967); while ‘Labrador tea’, L. groenlandicum Oeder of the Kwakiutl Indians is said to have ‘narcotic properties’ (Turner and Bell 1973). Similarly, the well-known ericaceous kinnikinnick, Arctostaphylos uva-ursi (L.) Sprenger, is smoked as an inebriant by Kwakiutl and other North American Indians (Ott 1993; Turner and Bell 1973), pointing to possible content of ericolin or grayanotoxins.Home
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