   Poisonous Plants in the Home, Landscape, and Beyond June 29, 2016 Jeff Schalau, Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County More than 700 species of plants located in the United States and Canada have caused illness or death in humans. In native plant populations, the presence of toxic compounds largely can be explained by natural selection. Plants containing toxic compounds are less likely to be grazed by animals and arthropods. Over time, less palatable (more toxic) plants in a given species’ population are more successful and the genes that produce these toxins are passed on to future generations. By the same process, animals and arthropods have also become more tolerant to low levels of toxins through time. Many vegetable plants also contain toxins. Selective breeding has decreased toxin content of vegetable crops to tolerable levels. For example, the stems and leaves of tomatoes, potatoes, peppers, and eggplant (members of the Nightshade family) contain glycoalkaloid toxins: the primary one being solanine. The edible fruits and tubers of these plants do not contain toxic levels of glycoalkaloids. However, potatoes may turn green in response to light exposure and become toxic. Nicotine is also a glycoalkaloid found in tobacco, another member of the Nightshade family. Many plants in our area are highly toxic when ingested. These include: castor bean (Ricinus communis); poison hemlock (Conium maculatum); and water hemlock (Cicuta douglasii). Castor bean is an introduced plant. Its seeds contain ricin, one of the most toxic compounds known, and can cause poisoning in livestock. Poison hemlock is also an introduced plant often found in wetland areas. All poison hemlock plant parts are toxic with the root being most toxic. An extract of poison hemlock was given to Socrates to carry out his death sentence in 399 BC. Water hemlock is a native plant to Arizona, is also found in wetlands. It looks similar to poison hemlock, but has a different toxin. These three plants are often considered the most highly toxic plants in Arizona if ingested. More information is available on these three species and other poisonous plants with the online edition (see URL below). Other poisonous plants can cause dermatitis. In the Verde Valley, we have poison ivy (Toxicodendron radicans) along the river, creeks and ditches. It is not common, but creek walkers should learn to recognize and avoid it. If you are exposed, try not to scratch. Wash and treat as recommended (see resources linked to the online edition). Most plants we use in our homes and landscapes were selected from wild populations for various qualities including foliage, flowers, and scent. In most cases, little or no consideration is given to a plant’s toxic qualities. In another sense, a poisonous landscape plant is also more resistant to herbivory by animals and arthropods which in turn could reduce wildlife conflicts and pesticide applications. Many of our commonly used landscape and houseplants are poisonous. Some of these are oleander, larkspur, foxglove, daffodil, lantana, narcissus, hyacinth, and dieffenbachia (again, see resources linked to the online edition). If there is a suspected human plant poisoning, immediately contact a physician or the Arizona Poison Control Center at 1-800-222-1222. Get a plant sample because it will aid in diagnosis and treatment. Answer all questions to the best of your knowledge, and follow the advice given by the Poison Control Center or physician. I recently attended a poisonous plants lecture by Dr. Tony Knight, semi-retired veterinarian. The lecture was excellent and he has published multiple books and journal articles on poisonous plants. Among these resources is A Guide to Plant Poisoning of Animals in North America. It is an excellent resource. Recently, he presented a lecture to the Arizona Mystery Writers. Can you guess why he was invited? Finally, don’t be overly paranoid. Just try to build your knowledge of local plant species and whether or not they are toxic. Cooperative Extension can assist in plant identification. Samples for identification should be fresh and include leaves, stem, flowers, and fruit for positive identification. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8992 or e-mail us at verdevalleymg@gmail.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Additional Resources Common Poisonous Plants and Plant Parts Texas A & M Agrilife Extension aggie-horticulture.tamu.edu/earthkind/landscape/poisonous-plants-resources/common-poisonous-plants-and-plant-parts/ Poisonous Plants in the Home Landscape Montana State University Extension msuextension.org/publications/YardandGarden/MT199902AG.pdf Castor Bean Texas A & M Agrilife Extension uvalde.tamu.edu/herbarium/forbs-common-name-index/castor-bean/ Poison Hemlock King County, Washington www.kingcounty.gov/environment/animals-and-plants/noxious-weeds/weed-identification/poison-hemlock.aspx Water Hemlock USDA Agricultural Research Service www.ars.usda.gov/Research/docs.htm?docid=9996 Poison Ivy Clemson Cooperative Extension www.clemson.edu/extension/hgic/pests/weeds/hgic2307.html  |