Above photo: Poison ivy has a compound leaf made of three leaflets. Photo by B. Rosie Lerner
Maybe you like to walk trails and visit natural areas. I do, too. However, it behooves us to consider the potential dangers of plants that can cause a nasty itch. Here are some of the main ones to look out for.
Poison ivy is perhaps the most common and best-known plant to avoid, resulting in blotching of the skin, burning water blisters, pain, and an intense itching sensation. Symptoms may be evident quickly, or appear within a few days.
Poison ivy is a 3-leaved plant. To be more accurate, each leaf has three leaflets that comprise the overall leaf. This botanical characteristic prompted the saying, "Leaves of three, let it be." It looks a lot like the leaves of the boxelder tree, making young boxelder seedlings and young poison ivy vines difficult to tell apart. However, poison ivy leaves are arranged alternately on twigs, while boxelder leaves are arranged oppositely. Poison ivy also has a vining habit over time – climbing and attaching to tree trunks or whatever is close by.
All parts of the plant contain and secrete a nonvolatile oil called urushiol (oleoresin), which affects the skin. The oil is not soluble in water, so washing with water alone does no good, and may spread the oil. Washing with a strong alkali soap is more effective, especially if done soon after exposure.
Don’t burn poison ivy after it has been cut or grubbed out and dried. The smoke from burning the plant contains particles that can cause serious injury to the eyes, skin, and respiratory tract.
A real mystery of nature is that some birds will eat poison ivy fruit (a greenish-white, smooth berry) without any complications (and then replant it elsewhere, with natural fertilizer added). Deer can also munch on poison ivy twigs.
Poison oak is a plant on the minds of some Hoosiers. It is a low-growing, non-climbing shrub with three leaflets, much like poison ivy. Although there have been unconfirmed reports of poison oak in Indiana, it is not known to occur in Indiana to date. According to the USDA-NRCS Plants Database, Atlantic poison oak has been confirmed in Illinois (Pope County, an extreme southern county), Tennessee, and West Virginia.
Poison sumac is a rare plant, generally found in or near wet areas and swamps. It can be about 6-20 feet tall, with compound leaves that have 7-13 leaflets and smooth margins. Hairless green berries turn gray-white when mature.
Poison hemlock is a weed of growing concern and increasing prevalence in Indiana. I wrote about it earlier this year. Poison hemlock looks a lot like wild carrot with fern-like leaves and small, white flowers in umbrella-shaped clusters; but unlike wild carrot, it has smooth green stems with purple blotching. It has become commonplace along roadsides, in pastures, and in some home landscapes. The largest threat of this weed is the toxicity of its alkaloids if ingested by livestock or humans, but it can also reduce the aesthetic value of landscapes and has been reported to creep into no-till corn and soybean fields as well. The plant’s alkaloids may be absorbed through the skin, so if you find yourself hand-pulling poison hemlock, it would be a good idea to wear gloves!
Other plants to avoid or be cautious around include cow parsnip, giant hogweed, stinging nettle, and spurges.
Two plants often confused with poisonous plants are fragrant sumac and Virginia creeper, both non-poisonous. Fragrant sumac has pubescent (hairy or fuzzy) leaves and red fruit. Virginia creeper, also called woodbine, is a common native vine with five leaflets.
For further information, find Purdue Extension publications at www.edustore.purdue.edu, from which I have sourced some of the above material.
Poison ivy has a compound leaf made of three leaflets. The top leaflet has a long stalk. Photo by B. Rosie Lerner