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Poison-Ivy/Poison-Oak/Poison-Sumac-The Virulent Weeds 1

LARRY W. MITICH2

I I; INTRODUCTION I, ii The word poison entered the English language in 1387 as 'poysoun" (18), and in Memoirs ofAmerican Academy of Arts and Sciences, v. 1, 1785, the word poison-ivy was used for the first time: "Poison ivy ... produces the same kind of inflammation and eruptions . . . as poison wood tree" (18). · The first known reference to poison-ivy, Toxicodendron radicans (L.) Ktze., dates from the 7th century in China and the 10th century in Japan. Since Toxicodendron species do not grow in Europe, the plants re­ mained unknown to Western civiliza­ tion until explorers visited the New World seven centuries later (7). Capt. John Smith (1579-1631) wrote the first description of poison-ivy and origi­ nated its common name; he noted a similarity in the climbing habit of They used that name for a shrub of the Southern States, North American poison-ivy to English with crenately-lobed, very pubescent leaflets (1). ivy (Hedera helix L.) (7). Toxicodendron, a pre-Linnaean name, was not accepted Joseph Pitton de Tournefort (1656-1708) established at the generic level by Linnaeus. Tournefort limited the the genus for poison-ivy in lnstitutiones rei herbariae, v. genus to ternate-leaved plants, thus omitting such close 1, p. 610, 1700 (7). The name is from the Latin for poison­ relatives of poison-ivy as poison-sumac and the oriental ous tree (9). lacquer tree (7). The lacquer tree has been known for In 1635 Jacques Philippe Cornut ( 1601-1651) wrote the first book on Canadian botany (Canadensium Plantarum thousands of years, and descriptions of the inflammations aliarumque nondum editarum historia, Parisiis [Paris]). produced by lacquer made from its sap go back to before This work is also the first one to illustrate poison-ivy Christ (17). (reproduced in this article), which he listed under the name Poison-ivy is also used figuratively for an unpleasant "Edera [Hedera] trifolia canadensis" (17). person. For example, B. Gray wrote in Miss Dynamite Linnaeus described poison-ivy in Hortus Ciffortianus (1939): "So this is the charming little prairie flower that ( 1737) as Rhus radicans; he later edited his description of Norman's fallen in love with! ... Primrose, my foot! Her the plant to include the climbing habit and added a descrip­ name's Poison Ivy" (18). tion of poison-oak, R. toxicarium (Salisb.) Gillis, when he In the U.S. there are· about 2 million cases of skin wrote Species Plantarum, 1753 (7). While Linnaeus re­ poisoning each year. Poison-ivy and its allies are the great­ corded 13 species of Rhus, 14 more had been assigned to est single cause of workers' compensation claims, and they the genus by the end of the 18th century, including species are a leading cause of field injuries among workers of the of Rhus, Toxicodendron, and others (7). Britton and Brown U.S. Forest Service (12). refer to R. toxicodendron as being "of American authors." During a single year in California, the working hours lost as a result of dermatitis and the discomfort experienced 1No. 50 of the series "Intriguing World of Weeds." by sensitive individuals make poison-oak the most hazard­ 2Ext. Weed Sci. Emeritus, Dep. Vegetable Crops, Univ. California, Davis, CA 95616. ous of all the poisonous plants in the state (5).

653 Weed Technology. 1995. Volume 9:653-656 J INTRIGUING WORLD OF WEEDS

CLASSIFICATION, fruit. The cashew nut is obtained from Anacardium occi­ Poison-ivy and poison-oak are neither ivy nor oak spe­ dentale; an oil obtained from its shell is valuable in resin cies. These plants, as well as poison-sumac, belong to the manufacture and, of course, the meat of the nut is a world­ cashew family, Anacardiaceae, and are known by several wide favorite. During the U.S. occupation of Japan follow­ local names. The leaf shape and growth habits of poison­ ing World War II, sensitized American soldiers ivy and poison-oak plants vary greatly throughout the U.S. unexpectedly suffered dermatitis when they inevitably Their common features are their poisonous nature and their came in contact with toilet seats and bars beautifully fin­ compound leaves, which consist of three leaflets. The old ished with Japanese lacquer (11). saying "Leaflets three, let it be" confirms the plant's nearly consistent leaf aspect (12). POISON-IVY Depending on area, poison-ivy, poison-oak, and poison- . Poison-ivy is one of two New Worl9 species; it also sumac are all generally known under the same name. The occurs in Eastern Asia. It is the most common and most proper classification of Toxicodendron has long been a widespread species in the Anacardiaceae. It is distributed bone of contention among botanists (11). Some classify from southern Canada to western Guatemala, the eastern poison-ivy and poison-oak, and infrequently poison-su­ third of the U.S. and throughout Mexico, on Bermuda, in mac, as varieties of one species, pointing out that all three the western Bahamas, Japan, western and central China have leaves divided into three ovate leaflets, variously and Taiwan, the Kurile Islands, and Sakhalin of Russia indented and lobed and downy beneath. And in June they (II). all bear slender clusters or panicles of inconspicuous Poison-ivy distribution in the U.S. is below the 44th greenish-white flowers in the axils of the leaves, followed parallel, extending from Maine to Florida and westward by clusters of small globular, greyish-white, waxy, berry­ into Nebraska, Kansas;Oklahoma, and Texas, It also grows like fruits (13). in a small area in southern Arizona and New Mexico (12). This very plasticity has given the "splitters" a chance to It is a low straggling shrub, sometimes occurring as a stout create more than 30 species! But the more conservative weedy vine climbing over trees. maintain that poison-ivy is a single variable species, with The compound leaves of poison-ivy are alternate on the several taxonomic varieties and forms (11, 14). Immu­ stem. Each leaflet is 5 to 10 cm long and is pointed at the nologically all species behave the same (17). tip. The supporting stem of the terminal leaflet is much In 1859, Darlington mentions both the erect and climb­ longer than the stems of the two lateral leaflets. Leaflets ing varieties of poison-ivy. Wrote he: "This species ... may be glossy or dull green and usually have smooth should not only be known to the farmer, but diligently surfaces. The edges of the leaflets vary considerably; some expelled from his premises" (4). George offered this ad­ are toothed or even lobed but most are not (12). vise: "Some fortunate persons are quite immune to the bad effects of the plant, and one of these might be hired to grub POISON-OAK it out and bum it" (6). The Anacardiaceae includes many widely distributed The Toumefort name Toxicodendron, a generic segre­ species which are both noxious and useful. The baleful gate of· Rhus, was chosen by Linnaeus as the specific species have in common the capacity to induce a severe epithet for poison-oak, R. toxicarium Salish. (7). Now contact dermatitis. All the dermatitogenic Anacardiaceae classified as T. toxicarium (Salish.) Gillis, this North are members of an immunologic cross reacting group American native shrub grows in dry woodland from New owing to biochemical similarities of their antigens. Sensi­ Jersey to Georgia and Texas, and the West Coast (13). tization to one carries with it the verdict of allergic reac­ Hickman uses T. diversilobum (Torrey & A. Gray) E. tivity to the rest (11). Greene for Western poison-oak, a shrub which can some­ Some dermatitis-producing Anacardiaceae possess time become tree-like (8). The common name is related to amiable or economically useful properties. The Orientals the typical leaflet shape, which resembles a white oak leaf prepare a rich furniture lacquer from R; verniciflua, the (7). ' lacquer tree; the marking nut or Indian ink tree, Semecar­ Poison-oak is very common in California, western Ore­ pus anacardium, is used to stain clothing, often as a laundry gon, and western Washington. It becomes a dense leafy mark. The mango, Mangifera indica, produces a delectable shrub when growing in the open or in filtered sun, but in

654 Volume 9. Issue 3 (July-September) 1995 WEED TECHNOLOGY shaded areas, as in coast redwoods, it becomes a tall-climb­ Both poison-ivy and poison-oak may cause severe der­ ing vine. Foliage turns a striking bright orange or scarlet matitis on contact; even breathing smoke from burning in the fall (3). plants is harmful (3). Transmission from smoke is by droplets on particles of dust and ash in the smoke, rather POISON-SUMAC than from gas. Smoke from burning poison-ivy plants or contaminated articles can carry the poison in a dispersed The generic name for sumac is Rhus; it is from the Greek form (13). rhous and the Latin rhus, both being names for sumac. The With time, sensitivity to poisoning can change. Gener­ Greek rhous is from rhodos, red, which gave rise to the ally, persons repeatedly exposed to poison-ivy and poison­ Celtic rhudd, red, the prevailing color of the sumac fruit oak become more sensitive because they react to lower (4, 9). concentrations of the oily toxicant. And people usually There are approximately 150 species of Rhus which are become less sensitive as they get older. But this rule does native to the temperate and subtropical regions of North not always hold true. Persons who have waded through and South America. It is a rather baffling genus, consisting patches of poison-oak numerous times without effect can of deciduous and evergreen trees, shrubs, sub-shrubs, and suddenly develop a severe rash after such contact. Occa­ several climbing plants (13). Rhus species occur in every sionally a person becomes less sensitive after a serious bout state of the Union (11 ). of poisoning by such plants ( 12). The dermatitis rarely lasts Poison-sumac, T. vemix (L.) Ktze., is poisonous to the longer than IO days (5). touch. Growing up to 7 m tall, it is found in swampy The plant sap contains urushiol, a yellowish slightly ground, from Quebec and Minnesota, south to Florida and volatile oil that causes the allergic reaction on the skin. Texas. Its milky juice was also used to induce blistering, Contacting the oil sets off a skin eruption that can vary from and for finishing boots and shoes. Its other common names a simple itching inflammation to water blisters, which include poison elder, poison dogwood, and poison ash (2, exude serum in the most severe cases, making infection a 13). real danger (5, 12). Urushiol is carried in specialized vessels or resin ducts DERMATITIS in the phloem of the plants. It normally is not present on The recorded history of poison-ivy dermatitis began in the surface of leaves or twigs nor in the stamen or the pollen 1609. In his account of his experiences with poison-ivy in of the flowers. It is found within the resin ducts in leaves Virginia and Bermuda, Capt. John Smith wrote: "The and flowers, and the bark of stems and roots in all Toxi­ poisoned weed is much in shape like our English ivy, but codendron species. When the leaves are bruised, chewed being touched, causeth redness, itching, and lastly, blisters, by insects, or otherwise damaged, then and only then will and which, howsoever after a while pass away of them­ the poison exude from the poison ducts onto the leaf selves, without further harm; yet because for the time they surface. The fluid changes in a few hours to a black gummy are somewhat painfill, it hath got itself an ill name, al­ substance (12). though questionless of no ill nature" (11). Indeed, Toxi­ Urushiol can be toxic for an indefinite period; several codendron sensitivity is doubtlessly the prototype of 100-year-old herbarium specimens have been toxic to sen­ allergic contact dermatitis in the U.S., having afflicted the sitive persons who have handled them (12). Contrary to very first white settlers (11). many old wives' tales, eating a poison~ivy leaf does not Lack of recognition of the plant in all its forms is the confer immunity (7). chief cause of exposure (10). Only humans and closely Objects such as clothing, gloves, and tools can convey related primates get the dermatitis (5). the poison. Once contaminated they are often the sources Symptoms from the first exposure to the allergen in the of prolonged infections. Dogs, cats, and livestock fre­ various species of Toxicodendron are extremely rare. Prob­ quently contact the plants and transmit the poison to chil­ ably seven out of every 10 people in the U.S. can develop dren or other unsuspecting persons. The poison can remain this allergy if exposed to the toxin a second time. With on the hair of animals for a considerable time after they subsequent exposures, however, symptoms may develop have gone through patches of poison-ivy (12). 12 to 72 hours later or in less time in highly sensitive Cattle, horses, sheep, hogs, and other livestock appar­ individuals (12). ently do not suffer skin irritation from these plants, even

Volume 9, lssue 3 (July-September) 1995 655 INTRIGUING WORLD OF WEEDS though they graze on them occasionally. Poison-ivy is son-ivy sap mixed with deer's blood and charcoal from a heavily browsed by deer. Bees collect nectar from the lightning-struck tree, the ·latter probably a black magic flowers, but no ill effects from contact with honey have connection. The Navahoes also used poison-ivy for good been reported (12). luck in gambling: they chewed a small piece of leaf and gave it to an opponent. The Karok Indians used sticks of r MEDICINAL PROPERTIES diversilobum to spit salmon steaks while smoking them, and its leaves to cover soaproot (Chlorogalum pomeridi­ Inconceivably, in North American medicine the acrid anum Kunth) when baking it in an earthen oven. The juice from fresh leaves of poison-oak was formerly pre­ Concow Indians of northern California even mixed the scribed for its "irritant, ruberfacient, stimulant and nar­ leaves of T. diversilobum into their acorn meal when they cotic" principles "in palsies, paralysis, drowsiness, baked bread. Other northern California tribes simply stupors, delirium, rheumatism, stiffness, herpetic troubles wrapped their meal in its leaves while baking. Some, too, [and] certain other eruptive diseases" as a "visicant for used its supple stems as the warp in weaving baskets (7). producing blisters." At one time poison-oak was officially The Yuki tribe of California used sap from T. diver­ listed in the Pharmacopoeia of the U.S. Although the plant silobum to get rid of warts: they would cut off the wart and was introduced into England in the 1640s, it was not used apply poison-oak to the wound. The same treatment was in medicine there until the end of the 18th century when it applied to ringworm and rattlesnake bites. They also used was utilized in the treatment of stubborn herpetic eruptions the sap, mixed with mountain hemlock and suet, for tribal (13). markings (7). The sap from poison-oak leaves has irritant, narcotic, and stimulant principles, and in small doses is a nervous system sedative. A tincture of the sap is used for relieving LITERATURE CITED nettle stings, ringworm, eczema, and rheumatism (13). I. Britton. N. L. and A. Brown. 1898. An. Illustrated Flora of the Northern United States, Canada and the British Possessions. Volume 3. Charles SEED DISSEMINATION Scribner's Sons, New York. 2. Brizicky, G. K. 1962. The genera of Anacardiaceae in the southeastern United States. J. Arnold Arbor. 43:359-375. At least 55 species of birds are responsible for the wide 3. Clark, D. E., ed. 1981. Sunset New Western Garden Book. Lane Publishing distribution of poison-ivy seed (15). After eating the fruits Co., Menlo Park, CA 512 p. of T. radicans, the seeds are voided near trees, fences, and 4. Darlington, W. 1859. American Weeds and Useful Plants. Orange Judd & Company, New York. 460 p. telephone lines ( I 0). Because of this, the pest is increasing 5. Fuller T. C. and E. McClintock. 1986. Poisonous Plants of California. throughout the country since the plant is usually left un­ University of California Press, Berkeley. 433 p. 6. Georgia, A. 1942. Manual of Weeds. The Macmillan Co., New York. 593 p. molested in such areas (6). 7. Gillis, W.T. 1971. The systematics and ecology of poison-ivy and the poison-oaks. Rhodora 73: 161-237, 370-443 465-540. 8. Hickman, J. C. 1993. The Jepson Manual, Higher Plants of California. ORNAMENTAL USES University of California Press, Berkeley. 1400 p. 9. Jaeger, E. C. 1944. A Source-book ofBiological Names and Terms (2nd Ed.). Poison-ivy has other economic significance. Hard to Charles C. Thomas, Springfield, IL. 257 p. believe, but poison-ivy has been cultivated in gardens in 10. Kingsbury, J.M. 1964. Poisonous Plants of the United States and Canada. Prentice-Hall, Inc., Englewood Cliffs, NJ. 626 p. New South Wales, Australia, and in Dunedin, New Zea­ 11. Klingman, A. M. 1958. Poison ivy (Rhus) dermatitis. A.M.A. Arch. Der­ land, and sold as an ornamental by English nurserymen, mat. 77: 149-180. probably as far back as 1640. Colorful autumnal foliage is 12. Klingman, D. L., D. E. Davis, E. L. Knake, W. B. McHenry, J. A. Meade, and R. E. Stewart. 1983. Poison Ivy, Poison Oak, and Poison Sumac. USDA, used to highlight displays of fruit at shows-and it does Ext. Serv., Washington, DC. 16 p. not escape cultivation! (16). 13. LeStrange, R. 1977. A History of Herbal Plants. Angus and Robertson, Publishers, London. 304 p. 14. Mabberley, D. J. 1989. The Plant-Book. Cambridge University Press, Cam­ NATIVE AMERICAN USES bridge. 706 p. 15. Martin, A. C., H. S. Zim, and A. L. Nelson. 1951. American Wildlife and Various American Indian tribes had intriguing uses for Plants. McGraw-Hill Book Co., New York. 500 p. 16. Petrides, G. A. 1958. A Field Guide to Trees and Shrubs. Houghton Miffiin, poison-ivy and its allies. The Meskwaki, Ojibwe, and Boston. 431 p. Potawatomi used it as a poultice on a swelling to make the 17. Rostenberg, A. M., Jr. 1955. An anecdotal biographical history of poison ivy. A.M.A. Arch. Dermal. 72:438. skin open (7). 18. Simpson, J. A. and E. S. C. WeineF. 1989, The Oxford English Dictionary, The Ramah Navahoes made an arrow poison from poi- 2nd Ed. Clarendon Press, Oxford.

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