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Scientific name: Anthophyta: Dicotyledonae: Sapindales: Anacardiaceae:
Common Name: Information Sheet, Poison Ivy
Photographer: E. M. Barrows
Identifier: J. Swearingen
The itchy rash from Poison Ivy on this biologist's hands is starting to abate.
GU Forest Ecology Organism Information Sheet (1998, last updated August 2008, E. M. B.)
Domain Eukarya: Kingdom Plantae: Group Seed Plants: Group Angiospermae: Group Dicotyledonae: Phylum: Anthophyta: Family Anacardiaceae (Cashew Family)
Rhus radicans (Linnaeus) Kuntze, Toxicodendron radicans, Bois de Chien, Herbe à la Puce, Cow-itch, Poison-ivy*, Poison Ivy (not a recommended name), Markry, Mercury
(I write the English name as Poison-ivy to indicate by the hyphenation that this species in not a true ivy in the genus Hedera following Shetler and Orli 2000).
I. General Information
A. What is the etymology of Poison-ivy?
(Greek, Latin Rhus , the old name for this genus; Latin radicans , rooting from its aerial roots)
B. What is the taxonomy of Poison-ivy?
C. What is the native range of Poison-ivy?
(Much of the Conterminous US, southern Canada.)
D. How long can a Poison-ivy plant live?
(Possibly decades, centuries.)
E. What are the general characteristics of Poison-ivy?
( Poison-ivy is a woody plant with many growth forms, e.g., a puny vine, a viney bush, a small vine, a very robust vine (up to 120 feet long) with side branches that look like tree branches. Some biologists designate some of the forms as separate species. Foster and Caras (1994, 172) split Rhus radicans of eastern U.S. into three species of Toxicodendron: Eastern Poison-oak (branching shrub), Poison-ivy (vine), and Rydberg's Poison-ivy (unbranching shrub). These authors list only a few of the many habits of Poison-ivies. Some researchers have designated over 30 species of Poison-ivy (Fernald 1950, 978).)
F. What are the characteristics of Poison-ivy stems.
(Green when young, brown with furrowed bark when old)
G. What are the characteristics of Poison-ivy leaves?
(Each leaf usually has three somewhat through highly shiny leaflets, reddish in spring; bright red, yellow, or both in fall, and green the rest of the warm season)
H. What are the characteristics of Poison-ivy flowers?
(small light green through light yellow, in a cluster)
I. What are the characteristics of Poison-ivy fruits?
(Small drupes, green turning whitish with maturity, indeshiscent)
J. What are the characteristics of Poison-ivy seeds?
K. What are the characteristics of Poison-ivy roots?
(In some forms, the roots often extend from stems and hold plants to trees and other substrates.)
II. Ecological Roles
A. What are general ecological roles of Poison-ivy in forests?
(Poison-ivy is an autotroph that lives in forests, forest edges, fields, successional areas, yards, and other terrestrial environments. Many kinds of organisms consume dead and living Poison-ivy fruits, leaves, roots, and stems.)
B. What are specific ecological roles of Poison-ivy in US forests?
(Poison-ivy competes with other plants for resources, in part, by growing on and over them. However, Poison-ivy generally does not form dense mats of vegetation over other native plants that can harm (and even kill) the plants as do the rampant aliens Asiatic Bittersweet and Porcelainberry in the Washington, D.C., Area. Poison-ivy is food of many organisms. Its leaf, root, and stem feeders (parasites) include 2 aphid spp., 1 beetle sp., 1 borer sp., 5 moth spp., 1 pysillid sp., 1 sawfly sp., and 8 scale spp. (Horst 1990; Westcott 1973, 601) and 1 leafminer (personal observation, 1998). I have seen certain diseases on Poison-ivy: galls (WDC, 1996), stunting and deforming of leaves (Eastern Shore, MD, 1996). A large sawfly (Arge), with beautiful red-and-black adults, consumes this plant. Mammals eat Poison-ivy leaves and stems. Poison-ivy shares pollinators with other forest plants. Nectar and pollen feeders (parasites, pollinators, predators) include many kinds of arthropods (beetle spp., butterfly spp., other bee spp., flower-fly spp., other fly spp., moth spp., and wasp spp.). Honey Bees make honey from its nectar. This is a minor plant in the continental U.S. (Pellett 1978). Fruit feeders include many bird species and several mammal species, some of which are major seed dispersers (Kricher and Morrison 1988, 119).)
III. Other Information
A. How do Humans use Poison-ivy?
(Some people with enough yard space grow Poison-ivy as an ornamental vine. Some people make money by controlling Poison-ivy and its symptoms; this includes making, selling, and using herbicides and other means of control and manufacturing and selling medicines for Poison-ivy. In a place where it does not contact people, Poison-ivy is a highly attractive, desirable, beneficial, ornamental plant.)
E. Is Poison-ivy dangerous to Humans?
(Yes, see below.)
Be sure to recognize Poison-ivy in its many appearances, and avoid it if you are susceptible to it. About 2,000,000 people get painful dermatitis from this plant each year in the U.S. (Foster and Caras 1994, 172). All plant parts contain urushiol (= toxicodendrol, an irritant, nonvolatile, phenolic oil) (Foster and Caras 1994, 172). Urushiol is found in resin canals and is released when the plant is bruised, even slightly. Symptoms are a light through heavy dermatitis which includes blistering, itching, redness, and swelling. Similar irritation occurs from eating the fruit or inhaling smoke from burning Poison-ivy. Some people are hospitalized, given shots, or both for Poison-ivy poisoning. The plant can be more dangerous in spring and summer when sap is abundant than at other times of the year. People who do not contract Poison-ivy as children, are often immune to it as adults. This immunity can disappear. People who get Poison-ivy show different degrees of susceptibility throughout their lives depending on their amounts of exposure, states of their immune systems, etc. People obtain rashes from contacting Poison-ivy directly, contacting articles with its urushiol (clothes, pet fur, shoes, etc.), and contacting smoke with its oil. If you contact Poison-ivy, wash your contacted areas with detergent (e.g., brown laundry soap), or at least regular soap, as soon as possible. Skin irritation can start several hours after contact with Poison-ivy. I got a bad case of Poison-ivy on my left ankle in 2002 after doing field work in a forest and a light case in 2008 after I removed some Poison-ivy from my yard. Some people report that fluid from Poison-ivy blisters does not cause more rash and blisters. In some cases, the rash appears to spread on a persons body after he initially contacts Poison-ivy; however, if a person does not recontact Poison-ivy directly, it is likely that later outbreaks are from very light amounts of urushiol during his initiation contact or from urushiol on clothing, shoes, or other items that he contacts. Bad cases of Poison-ivy rash often require an M.D.s care.
Fernald, M. L. 1970 (1950). Gray's Manual of Botany. Eight Edition. Corrected Printing. American Book Company, New York, NY. 1632 pp.
Foster, S., and R. Caras. 1994. A Field Guide to Venomous Animals and Poisonous Plants: North America North of Mexico. Houghton Mifflin Company, Boston, MA. 244 pp.
Horst, R. K. 1990. Westcotts Plant Disease Handbook. Van Nostrand Reinhold, NY. 952 pp.
Kricher, J. C. and G. Morrison. 1998. Eastern Forests. Houghton Mifflin Company, Boston, MA. 488 pp.
Pellett, F. C. 1978. American Honey Plants. Fifth Edition. Dadant and Sons, Hamilton, IL. 467 pp.
Shetler, S. G. and S. S. Orli. 2000. Annotated Checklist of the Vascular Plants of the Washington-Baltimore Area. Part I. Ferns, Fern Allies, Gymnosperms, and Dicotyledons. Smithsonian Institution (National Museum of Natural History, Department of Botany), Washington, D.C. 186 pp.
Westcott, C. 1973. The Gardener's Bug Book. Fourth Edition. Doubleday and Company, Garden City, NY. 689 pp.
* Required name. For full credit, please capitalize and spell the name correctly on your exam.
Disclaimer and warning. This course does not advise people to consume any study organisms. Should you do so, you do so at your own risk.