Western Poison-oak
Encyclopedia
Toxicodendron diversilobum, western poison oak or Pacific poison-oak (syn. Rhus diversiloba) is in the Anacardiaceae
family (the sumac family) and is a plant best known for its ability to cause allergic rashes after contact. Western poison oak is found only on the Pacific Coast
of the United States
and of Canada
.
It is extremely common in that region, where it is the predominant species of the genus; the closely related Atlantic poison oak (T. pubescens) occurs on the Atlantic Coast
.
. It is one of California's most prevalent woody shrubs, but also climbs, vine
-like, up the sides of trees, and can be found growing as single stems in grassland, often as part of early stage succession where woodland has been removed, and serving as a nurse plant
for other species.
The plant often occurs in California oak woodland
s and Douglas-fir
(Pseudotsuga) forests. The vine form climbs far up the trunks of coast redwoods, potentially killing smaller trees.
It is found in damp, semishady areas near running water and also thrives in direct sunlight, requiring water only in early spring. Any trail leading to a waterfall on California's coast may likely be home to western poison oak; it can also be found in some inland mountain ranges, such as the Cascades.
The plant alkaloid produced by members of the genus Toxicodendron, called urushiol, is known for causing an uncomfortable, and sometimes painful, skin reaction. Urushiol is the main component of the oily resin that is found on the stems and leaves of poison ivy and several other related species (Hogan, 2008). It causes contact dermatitis – an immune-mediated skin inflammation (Kalish et al, 1994) – in four-fifths of humans.
The active components of urushiol have been determined by Billets (1975) 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 (Billets et al, 1978).
Deer species and other animals predate on the leaves of the plant – which are rich in phosphorus, calcium and sulfur, while bird species utilize the plant structure for shelter (these animals do not seem to demonstrate any sort of reaction to urushiol) (Hogan, 2008). Furthermore, poison oak for example is widely distributed in western North America, inhabiting both forests and chaparral biomes (Hogan, 2008).
, which causes an allergic reaction
. Around 15% to 30% of people have no allergic response, but most, if not all, will become sensitized over time with repeated or more concentrated exposure to urushiol.
. It first causes severe itching, evolves into inflammation, colorless bumps, and then blistering when scratched. When in the skin, poison oak can be passed on. In late fall or winter, there are no leaves on the plants, so they can be difficult to recognize. People have occasionally used its branches to toast marshmallows or hot dogs over a campfire with results that sent them to the hospital.
in open sunlight, a tree with an 8–20 cm (3.1–7.9 in) trunk under conditions with ample sunlight, very wet winter/spring and dry summer, or as a climbing vine
in shaded areas. Like poison-ivy, it reproduces by creeping rootstocks or by seeds. The leaves are divided into three (rarely 5, 7, or 9) leaflets, 3.5 to 10 cm (1.4 to 3.9 in) long, with scalloped, toothed, or lobed edges - generally resembling the leaves of a true oak, though the western poison oak leaves will tend to be more glossy. Leaves are typically bronze when first unfolding, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink in the fall. White flowers form in the spring and, if fertilized, develop into greenish-white or tan berries. T. diversilobum is winter deciduous
, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of berries. Without leaves, poison oak stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried.
Botanist John Howell observed Toxicodendron diversilobums toxicity obscures its merits. "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."
1) http://onlinelibrary.wiley.com/doi/10.1002/jps.2600641032/abstract
Billets, S., Corbett, M. D. “Characterization of poison oak urushiol.” (1975). Journal of Pharmaceutical Sciences. Volume 64, issue 10, pgs 1715–1718.
2) http://globaltwitcher.auderis.se/artspec_information.asp?thingid=82914
Hogan, C. M. “Toxicodendron diversilobum: Western poison-oak.” (2008). Global Twitcher.
3) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC294319/
Kalish, S., et al. “Processing of urushiol (poison ivy) hapten by both endogenous and exogenous pathways for presentation to T cells in vitro.” (1994). JCI. Volume 93, no 5, pgs 2039–2047.
4) http://onlinelibrary.wiley.com/doi/10.1002/jps.2600670411/abstract
Billets, S., et al. “New GLC analysis of urushiol congeners in different plant parts of poison ivy, Toxicodendron radicans.” (1978). JPS. Volume 67, issue 4, pgs 483–485.
Anacardiaceae
Anacardiaceae are a family of flowering plants bearing fruits that are drupes and in some cases producing urushiol, an irritant. Anacardiaceae include numerous genera with several of economic importance. Notable plants in this family include cashew , mango, poison ivy, sumac, smoke tree, and marula...
family (the sumac family) and is a plant best known for its ability to cause allergic rashes after contact. Western poison oak is found only on the Pacific Coast
West Coast of the United States
West Coast or Pacific Coast are terms for the westernmost coastal states of the United States. The term most often refers to the states of California, Oregon, and Washington. Although not part of the contiguous United States, Alaska and Hawaii do border the Pacific Ocean but can't be included in...
of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and of Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
It is extremely common in that region, where it is the predominant species of the genus; the closely related Atlantic poison oak (T. pubescens) occurs on the Atlantic Coast
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...
.
Habitat
Western poison oak occurs only on the Pacific Coast of North America, where it is common, and ranges from southern Canada to the Baja California peninsulaBaja California Peninsula
The Baja California peninsula , is a peninsula in northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California. The Peninsula extends from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south.The total area of the Baja California...
. It is one of California's most prevalent woody shrubs, but also climbs, vine
Vine
A vine in the narrowest sense is the grapevine , but more generally it can refer to any plant with a growth habit of trailing or scandent, that is to say climbing, stems or runners...
-like, up the sides of trees, and can be found growing as single stems in grassland, often as part of early stage succession where woodland has been removed, and serving as a nurse plant
Ecological facilitation
Facilitation describes species interactions that benefit at least one of the participants and cause harm to neither. Facilitations can be categorized as mutualisms, in which both species benefit, or commensalisms, in which one species benefits and the other is unaffected...
for other species.
The plant often occurs in California oak woodland
California oak woodland
California oak woodland is a plant community found throughout the California chaparral and woodlands ecoregion of California in the United States and northwestern Baja California in Mexico...
s and Douglas-fir
Douglas-fir
Douglas-fir is one of the English common names for evergreen coniferous trees of the genus Pseudotsuga in the family Pinaceae. Other common names include Douglas tree, and Oregon pine. There are five species, two in western North America, one in Mexico, and two in eastern Asia...
(Pseudotsuga) forests. The vine form climbs far up the trunks of coast redwoods, potentially killing smaller trees.
It is found in damp, semishady areas near running water and also thrives in direct sunlight, requiring water only in early spring. Any trail leading to a waterfall on California's coast may likely be home to western poison oak; it can also be found in some inland mountain ranges, such as the Cascades.
The plant alkaloid produced by members of the genus Toxicodendron, called urushiol, is known for causing an uncomfortable, and sometimes painful, skin reaction. Urushiol is the main component of the oily resin that is found on the stems and leaves of poison ivy and several other related species (Hogan, 2008). It causes contact dermatitis – an immune-mediated skin inflammation (Kalish et al, 1994) – in four-fifths of humans.
The active components of urushiol have been determined by Billets (1975) 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 (Billets et al, 1978).
Deer species and other animals predate on the leaves of the plant – which are rich in phosphorus, calcium and sulfur, while bird species utilize the plant structure for shelter (these animals do not seem to demonstrate any sort of reaction to urushiol) (Hogan, 2008). Furthermore, poison oak for example is widely distributed in western North America, inhabiting both forests and chaparral biomes (Hogan, 2008).
Toxin
Western Poison oak leaves and twigs have a surface oil, urushiolUrushiol
Urushiol is an oily organic allergen found in plants of the family Anacardiaceae, especially Toxicodendron spp. . It causes an allergic skin rash on contact, known as urushiol-induced contact dermatitis...
, which causes an allergic reaction
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
. Around 15% to 30% of people have no allergic response, but most, if not all, will become sensitized over time with repeated or more concentrated exposure to urushiol.
Effects
Effects of poison oak are similar to those of poison ivyPoison ivy
Toxicodendron radicans, better known as poison ivy , is a poisonous North American plant that is well known for its production of urushiol, a clear liquid compound found within the sap of the plant that causes an itching rash in most people who touch it...
. It first causes severe itching, evolves into inflammation, colorless bumps, and then blistering when scratched. When in the skin, poison oak can be passed on. In late fall or winter, there are no leaves on the plants, so they can be difficult to recognize. People have occasionally used its branches to toast marshmallows or hot dogs over a campfire with results that sent them to the hospital.
Appearance
Western poison oak is extremely variable in growth habit and leaf appearance. It grows as a dense shrubShrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
in open sunlight, a tree with an 8–20 cm (3.1–7.9 in) trunk under conditions with ample sunlight, very wet winter/spring and dry summer, or as a climbing vine
Vine
A vine in the narrowest sense is the grapevine , but more generally it can refer to any plant with a growth habit of trailing or scandent, that is to say climbing, stems or runners...
in shaded areas. Like poison-ivy, it reproduces by creeping rootstocks or by seeds. The leaves are divided into three (rarely 5, 7, or 9) leaflets, 3.5 to 10 cm (1.4 to 3.9 in) long, with scalloped, toothed, or lobed edges - generally resembling the leaves of a true oak, though the western poison oak leaves will tend to be more glossy. Leaves are typically bronze when first unfolding, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink in the fall. White flowers form in the spring and, if fertilized, develop into greenish-white or tan berries. T. diversilobum is winter deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of berries. Without leaves, poison oak stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried.
Botanist John Howell observed Toxicodendron diversilobums toxicity obscures its merits. "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."
External links
- American Academy of Dermatology - Poison Oak info
- Western Poison-Oak Photo Gallery
- Poison Oak/Poison Ivy Information Center
1) http://onlinelibrary.wiley.com/doi/10.1002/jps.2600641032/abstract
Billets, S., Corbett, M. D. “Characterization of poison oak urushiol.” (1975). Journal of Pharmaceutical Sciences. Volume 64, issue 10, pgs 1715–1718.
2) http://globaltwitcher.auderis.se/artspec_information.asp?thingid=82914
Hogan, C. M. “Toxicodendron diversilobum: Western poison-oak.” (2008). Global Twitcher.
3) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC294319/
Kalish, S., et al. “Processing of urushiol (poison ivy) hapten by both endogenous and exogenous pathways for presentation to T cells in vitro.” (1994). JCI. Volume 93, no 5, pgs 2039–2047.
4) http://onlinelibrary.wiley.com/doi/10.1002/jps.2600670411/abstract
Billets, S., et al. “New GLC analysis of urushiol congeners in different plant parts of poison ivy, Toxicodendron radicans.” (1978). JPS. Volume 67, issue 4, pgs 483–485.