White berries? Beware!

Have you ever noticed white berries along your favorite hiking trail? Well, while some white berries are completely harmless, there is one white berry to be cautious of – those of Toxicodendron rydbergii, or western poison ivy. During the spring and summer, poison ivy is easily identifiable by the presence of “leaves in threes” or leaves comprised of three shiny leaflets. However, in the winter the leaves are gone, leaving only the white berries behind, and making it more difficult to identify.

Some people have a severe allergic reaction to poison ivy, while others have no or little response. An oily substance on the plants called urushiol causes this allergic reaction. The more exposure to poison ivy you have over time, the more severe your allergic reaction tends to be. Touching any part of the plant, even in winter, can cause a rash. Poison ivy is a member of the cashew or sumac family, Anacardiaceae. This is why many people with severe allergies to cashews also have severe allergic reactions to poison ivy.

Although the common name “poison ivy” is used, this name was first applied to the eastern poison ivy species, Toxicodendron radicans, because of the similarity in climbing habit with English ivy. Toxicodendron rydbergii is a low-growing shrub that does not climb at all. Other Toxicodendron species in North America include poison oak and poison sumac, neither of which are actual oaks or sumacs but whose leaves resemble these species.

See if you can (carefully!) locate some Toxicodendron rydbergii and help Denver Botanic Gardens by photographing as many plants as possible (carefully not to touch the plants!). Post your findings to iNaturalist so they will automatically be added to the Denver EcoFlora Project.

Posted on January 4, 2023 08:00 PM by jackerfield