''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 community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterrane ...

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 oaks.

Description

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

leaf A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

appearance. It grows as a dense tall shrub in open sunlight, a treelike

vine A vine ( Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") 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 thems ...

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 rhizomes and by seeds. Toxicodendron diversilobum foliage at Samuel P

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 leaves, usually in the autumn; to the shedding of petals, a ...

, 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 an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or '' pyrena'') of hardened endocarp with a seed (''kernel ...

. 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 state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

(

Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the wor ...

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

Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idah ...

, Washington, and

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...

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

Southeastern United States The Southeastern United States, also referred to as the American Southeast or simply the Southeast, is a geographical region of the United States. It is located broadly on the eastern portion of the southern United States and the southern po ...

. ''T. diversilobum'' and '' T. rydbergii'' (western poison ivy)

hybridize Hybridization (or hybridisation) may refer to: * Hybridization (biology), the process of combining different varieties of organisms to create a hybrid * Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals * ...

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 sta ...

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. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ...

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,

grassland A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...

s, and oak woodlands; and Douglas-fir (''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'' in the cypress family Cupressaceae (formerly treated in Taxodiaceae). Common names include coast redwood, coasta ...

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

Ecology

Black-tailed deer Two forms of black-tailed deer or blacktail deer that occupy coastal woodlands in the Pacific Northwest of North America are subspecies of the mule deer (''Odocoileus hemionus''). They have sometimes been treated as a species, but virtually all ...

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 squirrels, 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, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...

in agricultural fields, orchards, and vineyards. It is usually removed by pruning, herbicides, digging out, or a combination.

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, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...

. 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, 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 inflammation of the skin, 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. The area of skin involved can ...

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, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

controlled burn A controlled or prescribed burn, also known as hazard reduction burning, backfire, swailing, or a burn-off, is a fire set intentionally for purposes of forest management, farming, prairie restoration or greenhouse gas abatement. A contro ...

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 ringworm, is a fungal infection of the skin. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the area affected. Symptoms begin four to fourteen days after exposure. Multiple a ...

, and as a

poultice A poultice, also called a cataplasm, is a soft moist mass, often heated and medicated, that is spread on cloth and placed over the skin to treat an aching, inflamed, or painful part of the body. It can be used on wounds, such as cuts. 'Poultice ...

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 sedges. The family is large, with some 5,500 known species described in about 90 genera, the largest being the "true sedges" genus '' Carex'' ...

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 i ...

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 American people of the central and southern coastal regions of California, in portions of what is now San Luis Obispo, Santa Barbara, Ventura and Los Angeles counties, extending from Morro Bay in the north to Malib ...

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 (UK pronunciation: , US: ), 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. Complication ...

Cultivation

''Toxicodendron diversilobum'' can be a carefully situated component in wildlife gardens,

habitat garden A wildlife garden (or wild garden) is an environment created by a gardener that serves as a sustainable haven for surrounding wildlife. Wildlife gardens contain a variety of habitats that cater to native and local plants, birds, amphibians ...

s, and

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

. The plant is used in habitat restoration 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