Toxic Plants of North America

Toxic Plants of North America
by George E. Burrows and Ronald J. Tyrl
Iowa State University Press, 2001

Every animal on earth, humans included, owes its existence to the plant world. Grasses and trees and flowers and herbs form a living nucleus around which every ecosystem blossoms. We are rooted in flora everywhere.

And yet, the same families of plants that feed and shelter and provide medicinal potions for our bodies also include some of our worst enemies.

Lupines can be deadly to sheep. Certain fescues cause a "summer slump" in cattle and larkspurs kill thousands. Dogs that eat the fruit of lady-of-the-night or kiss-me-quick ornamentals may develop seizures that last for days.

Peach stones can kill humans. Yew berries, water hemlock, and oleander are also deadly. Consuming mountain peas, mayapples, raw kidney beans, excessive amounts of comfrey, or honey produced by bees in areas of flowering heath can make you sick to your stomach.

Plants in the St. John's-wort family include herbs that calm anxieties and ease depression in humans as well as weeds that cause photosensitization in grazing livestock, producing painful blisters and compromising meat, milk and wool production.

Detailed information on these toxic plants and hundreds more is contained in a massive compendium titled "Toxic Plants of North America," newly published by Iowa State University Press. Begun as a series of articles for "Oklahoma Veterinarian" on native plants toxic to livestock, this 1,350-page volume grew to include plants throughout North America poisonous to both domestic animals and humans. It is the most comprehensive reference of its kind now in print.

Each of 75 chapters is devoted to the toxic taxa of one family, from Aceraceae to Zygophyllaceae. The authors, George E. Burrows and Ronald J. Tyrl, have compiled information on the morphology and distribution of each plant as well as the disease problems it presents, the clinical signs of toxic exposure and the recommended treatments for poisoning.

An essential tool for veterinarians and extension agents, this book can also assist farmers and ranchers in identifying and avoiding potential problems. The text is complemented by margin notes that summarize common names, descriptions, poisoning threats and chemical structures. Line drawings and distribution maps are included to aid identification. 

Based on professional literature and their own personal observations, the authors offer historical and anecdotal accounts that help illustrate the problems associated with specific plants. Their entry on oak, for instance, includes this note:

"An excellent example of conditions forcing consumption of lethal quantities of oak foliage occurred in northern California in the spring of 1985 when an April snowstorm and cold weather forced cattle to consume oak buds rather than other forages. As a result, 2,700 calves from 60 ranches in 3 counties died."

"Toxic Plants of North America" is loaded with valuable information and curious insights into the relationships between the plant and animal kingdoms:

  • Monarch butterflies feed on milkweed to make themselves sickening to birds.
  • Grazing on horsebrush at bud stage can cause "bighead" in sheep, causing swelling of the face, ears and lips.
  • "Walking disease" in horses, first noted in the Walla Walla area of Washington, is caused by eating fiddleneck or burweed.
Many of these toxic interactions between plants and animals are poorly understood or just recently discovered. Much that was previously observed or learned at great expense was lost or went unrecorded. This volume documents, quite thoroughly, what we currently know about plant-caused problems in animals and what remains a mystery.

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Toxic Plants of North America
Covers toxic plants -- both wild and planted -- found on the North American continent north of the Tropic of Cancer. Covers both animal and human intoxications with pertinent information, including:
  • Plant morphology and distribution
  • Associated disease problems
  • Toxicants and their mechanisms of action
  • Clinical signs and pathological changes of intoxications
  • Treatment approaches
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