''Toxicodendron diversilobum'' (syn. ''Rhus diversiloba''), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family,

Anacardiaceae The Anacardiaceae, commonly known as the cashew family or sumac family, are a family of flowering plants, including about 83 genera with about 860 known species. Members of the Anacardiaceae bear fruits that are drupes and in some cases produce ...

. It is widely distributed in western North America, inhabiting conifer and mixed broadleaf forests, woodlands, grasslands, and

chaparral Chaparral ( ) is a shrubland plant plant community, community found primarily in California, southern Oregon, and northern Baja California. It is shaped by a Mediterranean climate (mild wet winters and hot dry summers) and infrequent, high-intens ...

biomes.C. Michael Hogan (2008)
"Western poison-oak: ''Toxicodendron diversilobum''"
, GlobalTwitcher, ed. Nicklas Strömberg Peak flowering occurs in May.iNaturalist: ''Toxicodendron diversilobum''
/ref> Like other members of the genus '' Toxicodendron'', ''T. diversilobum'' causes itching and allergic rashes in most people after contact by touch or smoke inhalation. Despite its name, it is not closely related to

oak An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...

s, nor is it a true tree.

Description

''Toxicodendron diversilobum'' is extremely variable in growth habit and

leaf A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...

appearance. It grows as a dense tall

shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...

in open sunlight, a treelike

vine A vine is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas, or runners. The word ''vine'' can also refer to such stems or runners themselves, for instance, when used in wicker work.Jackson; Benjamin; Da ...

and may be more than long with an trunk, as dense thickets in shaded areas, or any form in between.U.S. Forest Service: ''Toxicodendron diversilobum''
/ref> It reproduces by spreading

rhizome In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...

s and by seeds. Toxicodendron diversilobum foliage at Samuel P

The plant is winter

deciduous In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...

, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of mature fruit. Without leaves the stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried. The leaves are divided into three (rarely 5, 7, or 9) leaflets, long, with scalloped, toothed, or lobed edges.Jepson
/ref> They generally resemble the lobed leaves of a true oak, though tend to be more glossy. Leaves are typically bronze when first unfolding in February to March, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink from late July to October. White flowers form in the spring, from March to June. If they are fertilized, they develop into greenish-white or tan

drupes In botany, a drupe (or stone fruit) is a type of fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pip'' (UK), ''pit'' (US), ''stone'', or '' pyrena'') of hardened endocarp with a s ...

. Botanist John Howell observed that the plant's toxicity obscures its aesthetic values: ::In spring, the ivory flowers bloom on the sunny hill or in sheltered glade, in summer its fine green leaves contrast refreshingly with dried and tawny grassland, in autumn its colors flame more brilliantly than in any other native, but one great fault, its poisonous juice, nullifies its every other virtue and renders this beautiful shrub the most disparaged of all within our region.

Distribution and habitat

''Toxicodendron diversilobum'' is found in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

(

Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

was built on the site of a village named Yaangna or ''iyáanga’'', meaning "poison oak place"), the Baja California Peninsula,

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, Washington, and

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

. The related '' T. pubescens'' (eastern poison oak) is native to the

Southeastern United States The Southeastern United States, also known as the American Southeast or simply the Southeast, is a geographical List of regions in the United States, region of the United States located in the eastern portion of the Southern United States and t ...

. ''T. diversilobum'' and '' T. rydbergii'' (western poison ivy) hybridize in the

Columbia River Gorge The Columbia River Gorge is a canyon of the Columbia River in the Pacific Northwest of the United States. Up to deep, the canyon stretches for over as the river winds westward through the Cascade Range, forming the boundary between the state ...

area. ''Toxicodendron diversilobum'' is common in various habitats, from mesic

riparian zone A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripari ...

s to xeric chaparral. It thrives in shady and dappled light through full and direct sunlight conditions, at elevations below . The vining form can climb up large shrub and tree trunks into their canopies. Sometimes it kills the support plant by smothering or breaking it. The plant often occurs in chaparral and woodlands,

coastal sage scrub Coastal sage scrub, also known as coastal scrub, CSS, or soft chaparral, is a low scrubland plant community of the California coastal sage and chaparral subecoregion, found in coastal California and northwestern coastal Baja California. It is ...

grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...

s, and oak woodlands; and

Douglas-fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is the tallest tree in the Pinaceae family. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Or ...

(''Pseudotsuga menzesii''), hemlock–Sitka spruce, ''

Sequoia sempervirens ''Sequoia sempervirens'' ()''Sunset Western Garden Book,'' 1995: 606–607 is the sole living species of the genus ''Sequoia (genus), Sequoia'' in the cypress family Cupressaceae (formerly treated in Taxodiaceae). Common names include coast ...

''(coast redwood), '' Pinus ponderosa'' (Ponderosa pine), and mixed evergreen forests.

Ecology

Black-tailed deer Black-tailed deer or blacktail deer occupy coastal regions of western North America. There are two subspecies, the Columbian black-tailed deer (''Odocoileus hemionus columbianus'') which ranges from the Pacific Northwest of the United States and ...

mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whit ...

California ground squirrel The California ground squirrel (''Otospermophilus beecheyi''), also known as the Beechey ground squirrel, is a common and easily observed ground squirrel of the western United States and the Baja California Peninsula; it is common in Oregon and ...

s, western gray squirrels, and other indigenous fauna feed on the leaves of the plant. It is rich in phosphorus, calcium, and sulfur. Bird species use the berries for food, and utilize the plant structure for shelter. Neither native animals nor horses, livestock, or dogs demonstrate reactions to urushiol. Due to human allergic reactions, ''T. diversilobum ''is usually eradicated from

garden A garden is a planned space, usually outdoors, set aside for the cultivation, display, and enjoyment of plants and other forms of nature. The single feature identifying even the wildest wild garden is ''control''. The garden can incorporate bot ...

s and public landscaped areas. It can be a

weed A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. Pla ...

in agricultural fields, orchards, and vineyards. It is usually removed by pruning,

herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

s, digging out, or a combination. Poison oak is susceptible to infection by ''

Phytophthora ramorum ''Phytophthora ramorum'' is the oomycete known to cause the disease sudden oak death (SOD). The disease kills oak and other species of trees and has had devastating effects on the oak populations in California and Oregon, as well as being present ...

''.

Toxicity

''Toxicodendron diversilobum'' leaves and twigs have a surface oil,

urushiol Urushiol is an oily mixture of organic compounds with Allergic contact dermatitis, allergenic properties found in plants of the Family (biology), family Anacardiaceae, especially ''Toxicodendron'' ''spp.'' (e.g., poison oak, Toxicodendron vernic ...

, which causes an

allergic reaction Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food al ...

. It causes contact dermatitis – an immune-mediated skin inflammation – in four-fifths of humans. Most, if not all, will become sensitized over time with repeated or more concentrated exposure to urushiol. The active components of urushiol have been determined to be unsaturated congeners of 3-heptadecylcatechol with up to three double bonds in an unbranched C17 side chain. In

poison ivy Poison ivy is a type of allergenic plant in the genus '' Toxicodendron'' native to Asia and North America. Formerly considered a single species, '' Toxicodendron radicans'', poison ivies are now generally treated as a complex of three separate s ...

, these components are unique in that they contain a -CH2CH2- group in an unbranched alkyl side chain.

Exposure

''Toxicodendron diversilobum'' skin contact first causes itching; then evolves into

dermatitis Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened ...

with inflammation, colorless bumps, severe itching, and blistering. In the dormant deciduous seasons the plant can be difficult to recognize, however contact with leafless branches and twigs also causes allergic reactions. Urushiol volatilizes when burned, and human exposure to ''T. diversilobum'' smoke is extremely hazardous, from

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

controlled burn A controlled burn or prescribed burn (Rx burn) is the practice of intentionally setting a fire to change the assemblage of vegetation and decaying material in a landscape. The purpose could be for forest management, ecological restoration, ...

s, or disposal fires. The smoke can poison people who thought they were immune. Branches used to toast food over campfires can cause reactions internally and externally. Urushiol is also found in the skin of mangos, posing a danger to people sensitized to ''T. diversilobum'' when eating the fruit while it is still in the rind.

Uses

Medicinal

Californian Native Americans used the plant's stems and shoots to make baskets, the sap to cure

ringworm Dermatophytosis, also known as tinea and ringworm, is a mycosis, fungal infection of the skin (a dermatomycosis), that may affect skin, hair, and nails. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the a ...

, and as a

poultice A poultice or cataplasm, also called a fomentation, is a soft moist mass, often heated and medicated, that is applied to the skin to reduce inflammation, soothe pain, promote healing, or otherwise treat wounds or ailments. Soft materials like cer ...

of fresh leaves applied to rattlesnake bites.Univ. of Michigan, Dearborn – Native American Ethnobotany Database: ''Toxicodendron diversilobum''
/ref> The juice or soot was used as a black dye for

sedge The Cyperaceae () are a family of graminoid (grass-like), monocotyledonous flowering plants known as wikt:sedge, sedges. The family (biology), family is large; botanists have species description, described some 5,500 known species in about 90 ...

basket elements, tattoos, and skin darkening. An

infusion Infusion is the process of extracting chemical compounds or flavors from plant material in a solvent such as water, oil or alcohol, by allowing the material to remain suspended in the solvent over time (a process often called steeping). An inf ...

of dried roots, or buds eaten in the spring, were taken by some native peoples for an immunity from the plant poisons.

Chumash people The Chumash are a Native Americans in the United States, Native American people of the central and southern coastal regions of California, in portions of what is now Kern County, California, Kern, San Luis Obispo County, California, San Luis O ...

s used ''T. diversilobum'' sap to remove warts, corns, and calluses; to cauterize sores; and to stop bleeding. They drank a decoction made from the roots to treat

dysentery Dysentery ( , ), historically known as the bloody flux, is a type of gastroenteritis that results in bloody diarrhea. Other symptoms may include fever, abdominal pain, and a feeling of incomplete defecation. Complications may include dehyd ...

Cultivation

''Toxicodendron diversilobum'' can be a carefully situated component in

wildlife garden A wildlife garden (or habitat garden or backyard restoration) is an Biophysical environment, environment created with the purpose to serve as a sustainable haven for surrounding wildlife. Wildlife gardens contain a variety of habitats that cater t ...

habitat garden A wildlife garden (or habitat garden or backyard restoration) is an environment created with the purpose to serve as a sustainable haven for surrounding wildlife. Wildlife gardens contain a variety of habitats that cater to native and local plan ...

s, and

natural landscaping Natural landscaping, also called native gardening, is the use of native plants including trees, shrubs, groundcover, and grasses which are local to the geographic area of the garden. Benefits Maintenance Natural landscaping is adapted to t ...

. The plant is used in

habitat restoration Ecological restoration, or ecosystem restoration, is the process of assisting the recovery of an ecosystem that has been degraded, damaged, destroyed or transformed. It is distinct from conservation in that it attempts to retroactively repair ...

projects. It can be early stage

succession Succession is the act or process of following in order or sequence. Governance and politics *Order of succession, in politics, the ascension to power by one ruler, official, or monarch after the death, resignation, or removal from office of ...

where woodlands have been burned or removed, serving as a nurse plant for other species.

References

Gallery

Image:PoisonOakRedPhase.jpg, Red phase in spring File:Poison-oak-flowering.jpg, Green phase, and flowers Image:Toxicodendron_diversilobum_berries.jpg, Berries Image:Pacific-Poison-Oak.jpg, Summer–autumn turning color phase Image:PoisonOak wb smallerLeaves.jpg, Shrub form Image:ClimbingPoisonOak.jpg, Vine form

External links

U.S. Forest Service information: ''Toxicodendron diversilobum'' (Pacific poison oak)Calflora Database: ''Toxicodendron diversilobum'' (Pacific poison oak)Jepson Flora Project: ''Toxicodendron diversilobum''
* ttp://calphotos.berkeley.edu/cgi/img_query?where-taxon=Toxicodendron+diversilobum ''Toxicodendron diversilobum'' – U.C. Photo gallery {{Diseases of the skin and subcutaneous tissue diversilobum Flora of the West Coast of the United States Flora of Baja California Flora of British Columbia Flora of California Flora of Nevada Flora of Oregon Flora of Washington (state) Flora of the Cascade Range Flora of the Klamath Mountains Flora of the Sierra Nevada (United States) Natural history of the California chaparral and woodlands Natural history of the California Coast Ranges Natural history of the Central Valley (California) Natural history of the Channel Islands of California Natural history of the Mojave Desert Natural history of the Peninsular Ranges Natural history of the San Francisco Bay Area Natural history of the Santa Monica Mountains Natural history of the Transverse Ranges Plants used in traditional Native American medicine Taxa named by Asa Gray Taxa named by John Torrey Taxa named by Edward Lee Greene Flora without expected TNC conservation status