antispasmodic effect on the gastrointestinal tract, and they dilate the pupil of the eye. Poisoning from ingestion of plant parts or preparations thereof is relatively common and small quantities of the plant will produce observable adverse effects and even death (Cheeke, 1998). It has been calculated that 4 to 5 grams of leaf or seed of Datura is equivalent to a fatal dose for a child (Burrows and Tyrl, 2001). Most of these species have recently been shown to contain glycosidase inhibitory calystegines, as in the Solanum species.
The Taxaceae includes a number of Taxus species, all parts of which are acutely toxic to humans and livestock (Garland and Barr, 1998). The most extensive studies on toxicity have been conducted with the English yew T. baccata, native to Europe although it is widely grown as an ornamental plant in North America. Discarded clippings from a garden plant were recently reported to have resulted in the death of 43 cattle in a single night (Panter et al., 1993). Immediate fatalities are due to heart and circulatory failure, although less severely poisoned animals may show trembling, dyspnea, and collapse prior to succumbing (Garland and Barr, 1998; Kingsbury, 1964). The discovery of the Pacific yew T. brevifolia as a source of the anticancer drug, taxol, has stimulated extensive phytochemical examination of various Taxus species and over 100 diterpenoid taxanes have been characterized (Kingston et al., 2002).
Daphne species, members of the Thymelaeaceae, have been long recognized as poisonous plants. The most commonly seen is D. mezereum, cultivated as an ornamental, but also naturalized in some areas of the United States. The plants have attractive berries that have poisoned children, and it has been reported that only three berries each resulted in the death of six piglets (Kingsbury, 1964). Chewing on the bark has also caused fatalities in humans, and livestock have been killed by prunings from ornamental plantings (Burrows and Tyrl, 2001; Kingsbury, 1964). The toxic principles are daphnetoxins and mezerein, diterpenes of the phorbol ester type, which may also be cocarcinogenic and allergenic (Burrows and Tyrl, 2001).
The Verbenaceae contains Lantana species, which are toxic to sheep and cattle in Australia, South Africa, and the United States (Kellerman et al., 1988). Children are suspected of having been poisoned by consumption of the berries (Kingsbury, 1964). Principle among the poisonous species are L. camara and L. montevidensis (Burrows and Tyrl, 2001; Garland and Barr, 1998). Toxicity is highly variable, and in Australia there have been attempts made to classify the hazard on the basis of their flower color. Primary signs of acute poisoning in livestock is gastroenteritis, but in chronic poisoning secondary photosensitization due to liver damage may be appar-