root are also known causes of acute food-induced anaphylaxis (Pauli et al., 1988).
The Apocynaceae contains three genera (Apocynum, Nerium, and Thevetia) that are of concern because some species are acutely toxic to livestock and humans (Cheeke, 1998; Colegate and Dorling, 1994; Kellerman et al., 1988). Accidental poisoning of children has been frequent and it has been estimated that a single leaf of oleander (Nerium oleander) can be fatal (Cheeke, 1998; Everist, 1981; Keeler et al., 1978). The toxins are cardiac glycosides with symptoms similar to digitalis toxicity and may occur at up to 4 percent of the weight of the plant (Kingsbury, 1964).
Plant species in the Araceae that are toxic contain crystals of calcium oxalate (Cheeke, 1998; Everist, 1981; Keeler et al., 1978). In humans, this compound produces numbness of the mouth and throat (Cheeke, 1998; Keeler et al., 1978), resulting in the common name, dumbcane, for Dieffenbachia seguine. Death due to nephritis occurs on occasion in humans, but is more common in cats and laboratory animals (Burrows and Tyrl, 2001). Colocasia esculenta (taro, dasheen) leaves are generally recognized as being toxic (Burrows and Tyrl, 2001).
The Araliaceae is of concern primarily because of the species Hedera helix (English ivy), ingestion of the berries having been reported to poison children (Kingsbury, 1964). There have been occasional reports of poisoning in cattle when large amounts of the vine have been consumed, and the toxicity has been attributed to the saponin hederagenin (Kingsbury, 1964). In addition, H. helix contains the polyacetylene falcarinol, which also occurs in a number of species in the Apiaceae and is responsible for contact dermatitis in some individuals (Keeler and Tu, 1991). Falcarinol has structural affinities to the extremely toxic cicutoxin of water hemlock (Cicuta virosa). No toxicity appears to have been associated with the many other Hedera species. The only other potentially toxic species in the Araliaceae is the Devil’s walking stick (Aralia spinosa), which has been suspected of poisoning livestock (Kingsbury, 1964).
The Arecaceae encompasses a number of palm species growing in Asia and the Indian subcontinent. Betel nuts, the seeds of Areca catechu, are of concern, but the plant family is not considered to be of concern. Betel nuts are chewed when mixed with lime and wrapped in leaves of the betel pepper (Piper betle). This has a stimulant effect and produces slight intoxication. The seed contains approximately 0.45 percent of several tetrahydropyridine alkaloids, the primary active alkaloid being arecoline, an agonist of muscarinic acetylcholine receptors; it is used as an anthelmintic