Toxicodendron diversilobum - Poison oak
Family: Sumac Family (Anacardiaceae) [E-flora]
Other Names: Pacific poison oak [E-flora]
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Habitat / Range "Dry to mesic rocky slopes (often climbing trees) in the lowland zone; rare in SW BC, known from SE Vancouver Island, the Gulf Islands and Howe Sound; S to MX." [IFBC-E-flora]
Origin Status: Native [E-flora]
"toxicodendron diversiloba is a deciduous Shrub growing to 2.5 m (8ft 2in). It is hardy to zone (UK) 5 and is not frost tender. The flowers are dioecious (individual flowers are either male or female, but only one sex is to be found on any one plant so both male and female plants must be grown if seed is required) and are pollinated by Bees. The plant is not self-fertile. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils, prefers well-drained soil and can grow in nutritionally poor soil. Suitable pH: acid, neutral and basic (alkaline) soils. It cannot grow in the shade. It prefers moist soil." [PFAF]
"General: Deciduous shrub 1-2 m tall or woody climbing vine up to 15 m tall, glabrous to hairy, exuding milky juice when cut. [IFBC-E-flora]
"Leaves: Leaflets 3-5, rounded, obtuse or sometimes sharp-pointed at the tips, 3-7 cm long, turning scarlet in autumn. [IFBC-E-flora]
"Flowers: Inflorescence in loose, axillary, often reflexed panicles; flowers bisexual or unisexual, 1-2 mm long, yellowish-green; stamens exserted. [IFBC-E-flora]
"Fruits: Berrylike drupes, 5 mm long, white, glabrous. [IFBC-E-flora]
"Notes: Many people develop an itching or burning rash after contacting this plant because of its slightly volatile oil." [IFBC-E-flora]
Hazards
Urishol
"All parts of the plant contain resinous phenolic compounds known as urushiols. Direct contact with the plant, exposure to smoke or fumes from a burning plant or even contact with pets or animals that have touched the plant can cause severe allergic dermatitis in some individuals. There is usually a latent period of about 12 - 24 hours from the moment of contact, this is followed by a reddening and severe blistering of the skin. Even plant specimens 100 or more years old can cause problems(274)." [PFAF] See hazards section below for further information on Urishols
- Cooking Tool
- "The leaves were used by the Karok Indians of northwestern California to cover the bulbs of Soap Root, Chlorogalum pomeridianum, while baking them in the earth oven for food (see p. 6). The Concow Indians of Marysville Buttes mixed the leaves into their acorn meal when baking bread, and other tribes used the leaves to wrap the meal during the baking. Poison-Oak twigs were used to spit salmon steaks while they were being smoked." [EuCp]
- Tannin
- "The leaves are rich in tannin." [PFAF]
- Dye
- "Leaves can be collected as they fall in the autumn and used as a brown dye or as a mordant(169)." [PFAF]
- "An excellent black dye is obtained by exposing the sap to air(92)." [PFAF]
- "The fresh juice [stems, leaves, or roots] turns black quickly and was used in making an excellent black dye for basket materials. Some of the purest black strands in the baskets made by the Pomo Indians were dyed with this juice." [EuCp]
- Basketry
- "The supple stems are used as the warp in basket making(92). Slender stems are used as circular withes in basket making(257)." [PFAF] "More particularly among the northern tribes, the supple slender sterns were used for the warp or ground in woven baskets." [EuCp]
- Oil/Illuminant
- "An oil is extracted from the seeds(4). It attains a tallow-like consistency on standing and is used to make candles. These burn brilliantly, though they emit a pungent smoke(4)." [PFAF]
"Western poison oak was employed medicinally by some native North American Indian tribes who used it to treat various complaints[257]. In view of the potential toxicity of the plant, extreme caution is advised in any use of it. See the notes above on toxicity." [PFAF]
- Leaves
- Contraceptive: "A leaf has been swallowed in the spring as a contraceptive(257)." [PFAF]
- Dermatological: "A tincture of the fresh leaves has been used in the treatment of eczema and skin diseases[4]. It is also used in the treatment of warts, ringworm etc(92)." [PFAF]
- Snakebites: "A poultice of the fresh leaves has been applied to rattlesnake bites(257)." [PFAF] "Fresh leaves bound tightly over the bite of a rattlesnake were thought to counteract the poison, but this had to be done immediately." [EuCp]
- Leaf Buds
- "The leaf buds have been eaten in the spring in order to obtain immunity from the plant poisons(257)." [PFAF]
- Root
- "An infusion of the dried roots has been taken in order to give immunity against any further poisoning(257)." [PFAF]
- "A decoction of the roots has been used as drops in the eyes to heal tiny sores inside the eyelids and to improve vision(257)." [PFAF]
- Plant
- Warts: "The juice of the plant has been used as a treatment for warts(257)." [PFAF] Sap used medicinally to remove warts, corns, and calluses, to cauterize sores or skin cancers, to stop bleeding; root decoction drunk cold for dysentery. (0) [EthChumash] "A moxa of the plant has been used in the treatment of warts and ringworm(257)." [PFAF]
- Juice: "The juice from stems, leaves, or roots was used as a cure for warts and as a cure for ringworm." [EuCp]
"Succeeds in a well-drained fertile soil in full sun(200). Plants do not require a rich soil(11). The young growth in spring can be damaged by late frosts. Plants have brittle branches and these can be broken off in strong winds(200). Plants are also susceptible to coral spot fungus(11). This species is closely related to R. toxicodendron(1). Many of the species in this genus, including this one, are highly toxic and can also cause severe irritation to the skin of some people, whilst other species are not poisonous. It is relatively simple to distinguish which is which, the poisonous species have axillary panicles and smooth fruits whilst non-poisonous species have compound terminal panicles and fruits covered with acid crimson hairs(1, 4). The toxic species are sometimes separated into their own genus, Toxicodendron, by some botanists(200). Plants in this genus are notably resistant to honey fungus(200). Dioecious. Male and female plants must be grown if seed is required." [PFAF]
Propagation
"Seed - best sown in a cold frame as soon as it is ripe. Pre-soak the seed for 24 hours in hot water (starting at a temperature of 80 - 90c and allowing it to cool) prior to sowing in order to leach out any germination inhibitors(200). The stored seed also needs hot water treatment and can be sown in early spring in a cold frame(200). When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts. Cuttings of half-ripe wood, 10cm with a heel, July/August in a frame(200). Root cuttings 4cm long taken in December and potted up vertically in a greenhouse. Good percentage(78, 200). Suckers in late autumn to winter(200)." [PFAF]
Synonyms
- Rhus diversiloba Torr. & A. Gray [E-flora]
- Toxicodendron radicans subsp. diversilobum (Torr. & A. Gray) Thorne [E-flora]
TOXICODENDRON - POISON OAK, POISON IVY
"Shrub, vine-like or not; generally dioecious. Leaf: ± resinous;
leaflets 3–9, thin to ± leathery, entire, toothed, or lobed.
Inflorescence: raceme or panicle, axillary, ± open;
flowers pedicelled.
Flower: stamens 5, vestigial in pistillate flowers;
styles ± fused, stigmas 3.
Fruit: generally spheric, papery or leathery in age,
cream to brown; pulp resinous.
15 species: America, eastern Asia. (Latin: poisonous tree)
TOXIC: resin on leaves, stems, fruits causes severe contact dermatitis;
one of the most hazardous plants in California." [Jepson]
Local Species;
- Toxicodendron diversilobum - poison oak [E-flora]
Species Mentioned
T. pubescens and T. diversilobium. "occasionally these plants hybridize." [CPPM] Toxicodendron species including; T.diversilobum, T.pubescens, T.radicans, T.rydbergii, T.vernix [HPIP Shih]
Hazards
Toxin: "Urushiol, an antigenic catechol." [HPIP Shih]
Clinical Findings: "The rash often appears in a linear pattern consistent with brushing up against the plant. More than 50% of the population is sensitized to urushiol and will get rhus dermatitis on contact with a plant of this genus." [HPIP Shih]
"Management: Symptomatic and supportive care; this includes the potential use of topical or oral antihistamines and possibly corticosteroids. Consultation with a Poison Control Center should be considered." [HPIP Shih]
Urishol
"The full-blooded Indians seem to have been only slightly, or not at all, subject to the effects of this poison, though those with mixed blood often suffered as badly as their white fellows. Some are said to have eaten a small piece of the very young leaf in the early spring to prevent the poison from affecting them for the rest of the year. .... For remedies in cases of poisoning the Indians were taught by the early settlers to use such salts as baking-powder. Possibly the use of Soap Root, Chwrogalum pomeridianum, cooked and made into a paste was also learned from the white man. One of their original cures seems to have been a strong extract from the root of the Sunflower, Wyethia longicaulis, with which the inflammation was bathed." [EuCp]
"The sap of all parts of these species contains urushiols, the same irritating oleoresins and their derivatives that are found in poison ivy (*Toxicodendron radicans*, *T. rydbergii*) and poison sumac (*T. vernix*). Most people are allergic to these substances to some degree, and on contact break out in a burning, itching rash." [CPPM]
"Inside the undamaged plant, urushiol is a transparent oil." [TNS]
"Although the chemical structure of urushiols differs between various species, sensitization to one species of Toxicodendron usually results in cross - sensitivity to other Toxicodendron species." [TNS]
"In moist aerobic environments, urushiol oxidizes and polymerizes to form a brown - black lacquer. The sap from poison ivy, poison oak, and poison sumac turns dark brown within about 10 minutes and black by about 24 hours.28 Urushiol adheres to many surfaces, including gloves, skin, clothes, equipment, and animal fur. Because of the solubility of catechols in rubber, urushiol penetrates rubber gloves, but not heavy - duty vinyl gloves.29 Soap and water degrade urushiol, and a thorough machine washing removes dried urushiol from clothes. Once the urushiol - protein complex forms in the skin, washing will not reduce the antigenicity of the complex. Urushiol is nonvolatile; therefore, airborne contact dermatitis occurs only when smoke carries the urushiol on dust particles." [TNS]
"Urushiol occurs throughout poison ivy and poison oak plants including the stems, roots, leaves, and vines. During the fall, the red, brittle leaves contain high concentrations of urushiol. In the winter season, the bare twigs of poison oak and poison ivy retain significant concentrations of urushiol in the sap. In a study of seasonal urushiol content of poison oak leaves, the urushiol content remained relatively stable (0.02 – 0.4%) from Spring to early November, when the urushiol content increased to 0.9 – 2.6%.30 By December when the leaves fell, the urushiol content was low; therefore, fallen leaves are not allergenic." [TNS]
Susceptible Populations
"Of all members of the animal kingdom, only humans and some other primates are sensitive to Toxicodendron species. ...about 50% of the adult population develop hypersensitivity dermatitis following a transient contact (i.e., approximately 2.5μ g purifi ed urushiol) to Toxicodendron species.33 Increasing the dose of urushiol to 50μ g produces contact dermatitis in an additional 30 – 40% of the population. Consequently, about 15% of the population does not develop reactions to urushiol despite exposure to doses far exceeding the amount of urushiol normally present following exposure to Toxicodendron plants. ... The high incidence of urushiol sensitivity in children of urushiol - sensitive parents suggests a significant genetic predisposition.34" [TNS]
Clinical Response
"Typically, contact dermatitis produces a burning pruritic erythema over the area of contact in the configuration of linear scratch marks about 2 – 4 days after exposure to Toxicodendron species.35 Highly sensitized patients may react to contact with Toxicodendron species within 8 hours, and patients without previous skin lesions may require 5 – 6 days to react. New lesions can appear up to 14 days after exposure.36 The erythematous lesions progress to papules and vesicles. ...Rarely, black spots or linear lesions appear on the skin as a result of the deposition of urushiol on the skin that oxidizes and polymerizes to form a black lacquer.37 Nausea, vomiting, diarrhea, and abdominal pain may accompany the skin lesions in highly sensitive individuals. Typically, the skin lesions resolve within approximately 10 – 14 days. The development of new skin lesions 2 – 3 weeks after initial contact suggests re - exposure to antigen reservoirs (e.g., pets, equipment, tools, clothing, fingernails). Sensitivity to urushiol decreases with age. In general, the onset of the hypersensitivity reaction is longer and the severity of the reaction is milder in older patients compared with a similar exposure in younger individuals.38 The most common complication following the development of contact dermatitis is secondary infection." [TNS]
"Ingestion of leaves may produce a severe gastroenteritis and pruritus ani. ... Rarely, Toxicodendron species may produce urticaria, allergic rhinitis, and asthma." [TNS]
Decontamination
"Urushiol binds quickly to the skin (i.e.,< 30 – 60 minutes), and the skin should be rinsed immediately with cool water beginning with the hands or other contaminated areas first. Urushiol is neutralized by alkaline soap, such as ordinary face soap or dishwashing liquid (pH 8.8 – 10.5); the affected skin should be washed with soap and water after the initial rinse, particularly the palms of the hands.36 Vigorous scrubbing of the affected area should be avoided. Volunteer studies suggest that the removal of urushiol with soap or solvents reduces the severity of urushiol - induced lesions when initiated within 2 hours of exposure, but decontamination does not eliminate reactions in sensitized individuals.41,42 The use of an organic solvent [acetone, isopropanol,...] may leach some of the urushiol from the skin up to 4 – 6 hours after an exposure; however, further exposure to urushiol must be avoided immediately after the use of these solvents because these solvents reduce the protective skin lipids and the natural barrier to urushiol. Following the use of these solvents, the affected skin should be washed with soap and water to remove any urushiol remaining on the surface of the skin. The addition of hydrogen peroxide or sodium hypochlorite to the water increases the oxidation of urushiol. All clothing should be changed and the contaminated clothing washed with soap and water." [TNS]
Supportive Care
"Cold water compresses or soaks 3 – 4 times daily for 15 minutes are recommended for weeping or pruritic lesions during the acute phase." [TNS]
"All contaminated clothing and domestic animals should be washed with soap and water." [TNS]
Notes on other, similar species
(Wikimedia)4
(Wikimedia)5
Poison Ivy - Rhus toxicodendron [PDR]
Rhus toxicodendron L. is a synonym of Toxicodendron pubescens Mill. S[WFO]
Medicinal Parts: "The medicinal parts are the leaves collected after flowering and dried, the fresh young shoots, the young flowering branches and the fresh leaves." [PDR]
ACTIONS AND PHARMACOLOGY
COMPOUNDS
"Alkyl phenols: urushiol, chiefly cis,cis-3-(n-heptadeca- 8',H'-dienyl)catechol, cis,cis, cis-3-(n-heptadeca-8',ll\14'- trienyl)catechol, cis-3-(n-heptadec-8'-enyl)catechol" [PDR]
Tannins [PDR]
Flavonoids [PDR]
INDICATIONS AND USAGE
"Homeopathic uses: The drug is used to treat rheumatism in the joints and muscles; overexertion (stress and strain); febrile infections with giddiness; inflammation of the respiratory tract, gastrointestinal tract and the eyes; menstrual disturbances; anxiety and depressive states; and itching skin diseases." [PPDR]
PRECAUTIONS AND ADVERSE REACTIONS
"Contact with larger quantities of the allergen can bring about resorption and generalized erythema; in severe cases also fever and unconsciousness. Severe conjunctivitis and corneal inflammations, with possible loss of sight, may result after contact with the eyes. External application of the drug should be avoided. Skin affected by accidental contact should be intensively rinsed with a soapy solution and then cleaned with ether or ethanol. The points of inflammation should be covered with bicarbonate of soda paste (mixed with water). Internal treatment is carried out with systematically effective corticosteroids. Cooling bandages give relief in mild cases." [PDR]
Overdosage
"Overdoses of homeopathic preparations lead to severe mucous membrane irritation, accompanied by queasiness, vomiting, intestinal colic and diarrhea, as well as signs of resorption, e.g., vertigo, stupor, kidney damage (nephritis, hematuria)." [PDR]
"Following gastrointestinal emptying (gastric lavage with burgundy-colored potassium permanganate solution, sodium sulfate), installation of activated charcoal and shock prophylaxis (quiet,, warmth), the therapy for these sorts of poisonings consists of treating spasms with diazepam (i.v.), electrolyte substitution and treating possible cases of acidosis with sodium bicarbonate infusions. In case of shock, plasma volume expanders should be infused. Monitoring of kidney function is essential. Intubation and oxygen respiration may also be necessary. Furthermore, the leaves possess a very severe potential for sensitization, due to their urushiol content. Following sensitization (which can also occur through contact with decorative art from the Far East, such as wooden chairs that have been treated with toxicodendron lacquers), renewed contact leads within a few hours to itching eczemas and eventual blister formation." [PDR]
DOSAGE
Mode of Administration: "Homeopathic dilutions of the mother tincture." [PDR]
Homeopathic Dosage: "5 drops, 1 tablet or 10 globules every 30 to 60 minutes (acute) or 1 to 3 times daily (chronic); parenterally: 1 to 2 ml sc; acute: 3 times daily; chronic: once a day (HAB34); children are given different doses. Storage: In tightly sealed containers, not to be kept for more than a year." Details: [PDR]
- E-flora - http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Toxicodendron%20diversilobum[Accessed: 12/28/2014]
- PFAF - https://pfaf.org/user/Plant.aspx?LatinName=toxicodendron+diversilobum, Accessed June 12, 2019
- Jepson - John M. Miller & Dieter H. Wilken, except as noted, 2012. Toxicodendron, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=46791, accessed on May 12 2014
- WFO - 'WFO (2025): Rhus toxicodendron L. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-0000403073. Accessed on: 28 Oct 2025'
Image References
- 1, Walter Siegmund, CC BY-SA 3.0
- 2, Björn S..., CC BY-SA 2.0
- 3, Eeekster, CC BY-SA 3.0
- 4, Rawpixel, CC BY-SA 4.0
- 5, Pierre-Joseph Redouté, Public domain, via Wikimedia Commons