Here are an additional three plant species that contain known toxins and occur commonly in the U. S. and elsewhere. Each of these occurs in the wild but also in my yard.
Gelsemium– Two species of Gelsemium, (G. sempervirens and G. rankinii) are high-climbing forest vines of the Loganiaceae that are native to the southeastern states. A third species, G.elegans, is native to southeast Asia and used in traditional medicine in China and Japan. All parts of the Gelsemium plants, including nectar, contain toxic alkaloids (gelsemine, gelseminine and others up to a total of about 20). Some of the unnamed alkaloids appear to have value as anti-tumor, analgesic and anti-inflammatory agents at specified concentrations. However deaths associated with respiratory failure and paralysis have occurred in humans and livestock from consumption of Gelsemium. The alkaloids gelsemine and gelseminine. are structurally similar to strychnine, the well-known and deadly alkaloid derived from an Asian tree in the genus Strychnos, which belongs, like Gelsemium, to the Loganiaceae.
Honey made from Gelsemium nectar is deadly and deaths to children are reported to have occurred from eating the flowers. In the past, roots were used medicinally but many deaths resulted. Toxic effects would likely also be seen in pets if they chewed leaves. The foliage can also cause dermatitis. Fruits and seeds are undoubtedly toxic although in my experience they are hard to find on vines.
Surprisingly, low doses of gelsemine were experimentally shown to reduce anxiety in rats and possibly may reduce severe anxiety in humans! Gelsemine last made the news in 2012 when a Russian expatriate was lethally poisoned in London. The victim contained traces of the alkaloid in his stomach. The previous year a Chinese billionaire was alleged to have been poisoned by a rival who put G. elegans in the victim’s stew!
The three closely related species produce large yellow, trumpet-shaped flowers in spring and are readily available at garden shops where they are labeled as yellow or Carolina Jessamine. Generally the jessamine is sold by retailers without warning labels! Besides climbing tall trees, both American species (G. sempervirens is more common) may be found along shrubby roadsides, hedge-rows, fences and swamps in the southeastern states.
Phytolacca americana (of the Phytolaccaceae) is a very common and widespread large herbaceous plant found throughout the Northern Hemisphere. A related species, P.edulis, is native to China where it is harvested for food. Although often reaching or exceeding 3m (10 feet) in height in summer, the above-ground parts of P. americana (common name pokeweed) completely die back to ground level each year leaving the large subterranean rhizome to survive and produce new stems in spring. Although many poisonings, some lethal, of humans and livestock have occurred from consumption of the mature shoots (leaves and purple stem), and the rhizome, in spring, new shoots can be boiled and eaten without harm. In fact, they are esteemed in some areas of North America and pokeweed has been introduced to southern Europe where it is cultivated as a crop for its young shoots. However older shoots (stems and leaves), which turn purple, accumulate a toxic resin (phytolaccotoxin) in the bark along with the alkaloid phytolaccine, and a saponin. Saponins are glycosides that foam up when stirred and have been used as a fish poison and soap substitute. In the summer or autumn depending on latitude, pokeweed produces berries that turn purple when ripe and according to some authorities can, in the mature stage, be added to pies and eaten without harm. Other sources disagree. The berries also are sought by many frugivorous birds.
Crotolaria (Fabaceae) is a genus of herbaceous legumes that produces showy yellow flowers, followed by inflated pods within which the seeds develop and then dehisce (break loose) and knock about if the pod is shaken. Thus the common name rattlebox.
Later the pod opens releasing the small seeds. At least 11 species grow wild in Florida, of which four are native. Members of the genus are either trifoliate or simple-leaved. In my yard C. spectabilis appears every year since I initially scattered seeds haphazardly around the yard about five years ago. The introduced species (like C. spectabilis) originate from tropical America, Asia and Africa. These annuals are common as weeds in various disturbed sites, roadsides, abandoned farmland, etc. Introduced species tend to be larger but shorter-lived than the North American species. The species native to Florida are relatively uncommon, being restricted to flatwoods, sand hills and dunes.
Crotolarias are toxic to all livestock and fowl and likely would be to humans if ingested. The
livestock exhibit a range of pathological responses that can lead to death if the animals are allowed to continue ingesting the plant. Some or all species of Crotolaria contain pyrrolizidine alkaloids in all parts of the plant. Members of this group of alkaloids also are found in unrelated plants such as members of the genus Senecio (ragwort or groundsel). Ingestion of Senecio foliage has led to serious, even lethal, poisoning of humans. Contamination of grains by Senecio seeds has also caused poisoning.