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Overview

Brief Summary

Western Poison-oak (Toxicodendron diversilobum) is found at elevations below around 1650 m in westernmost North America from British Columbia (Canada) to Baja California (Mexico), including the U.S. states of Washington, Oregon, California, and Nevada. It may grow as a shrub (sometimes tree-like), 0.5 to 4 m tall, or (when externally supported) as a vine more than 30 m long--or any form in between (Gartner 1991a,b). The (typically) 3-leafleted leaves turn bright red in autumn. Poison-oak and its close relatives are well-known for possessing skin-irritating oil (urushiol), which can cause severe allergic reactions in humans.

The taxonomy and nomenclature of North American Toxicodendron has been in flux for over a century, largely due to confusing within-species variation in growth form, leaf and leaflet shape, and other features (e.g., Gillis 1971; Gartner 1991). This has resulted in an abundance of synonyms, but five species are now generally recognized: Common Poison-ivy (T. radicans), Western Poison-ivy (T. rydbergii), Eastern Poison-oak (T. pubescens), Western Poison-oak (T. diversilobum), and Poison-sumac (T. vernix) (Senchina 2006).

Senchina (2008) reviewed the literature on animal and fungal associates of Toxicodendron in North America with a particular eye toward identifying potential biological control agents. Interest in finding new ways to control poison-oak and its relatives may increase in coming years given data suggesting that these plants may become more abundant and more ‘‘toxic’’ in the future, potentially affecting global forest dynamics and human health (Mohan et al. 2006).

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Distribution

Occurrence in North America

     CA  OR  WA  MEXICO  BC

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Pacific poison-oak is distributed from Baja California north to British
Columbia [31,45,58].  It occurs west of the Cascade Range in Washington,
Oregon, and California [32] and is ubiquitous in California west of the Sierra
Nevada and the Mojave Desert [38].
  • 31.  Hickman, James C., ed. 1993. The Jepson manual: Higher plants of        California. Berkeley, CA: University of California Press. 1400 p.        [21992]
  • 32.  Hitchcock, C. Leo; Cronquist, Arthur. 1973. Flora of the Pacific        Northwest. Seattle, WA: University of Washington Press. 730 p.  [1168]
  • 38.  Kingsbury, John M. 1964. Poisonous plants of the United States and        Canada. Englewood Cliffs, NJ: Prentice-Hall, Inc. 626 p.  [122]
  • 45.  Munz, Philip A. 1974. A flora of southern California. Berkeley, CA:        University of California Press. 1086 p.  [4924]
  • 58.  Thilenius, John F. 1968. The Quercus garryana forests of the Willamette        Valley, Oregon. Ecology. 49(6): 1124-1133.  [8765]

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Regional Distribution in the Western United States

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

    1  Northern Pacific Border
    2  Cascade Mountains
    3  Southern Pacific Border
    4  Sierra Mountains

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Physical Description

Morphology

Description

More info for the terms: shrub, vine

Pacific poison-oak is a many-stemmed, deciduous, native shrub or woody vine.
Shrubs are erect with stems from 2 to 6 feet (1-2 m) tall.  Vine stems
commonly reach 10 to 30 feet (3-10 m), but may be as long as 100 feet
(30 m) [22].  As a vine, Pacific poison-oak climbs trees or other support by
adventitious roots and/or wedging stems within grooves or crevices of
the support [7,22,62].  The bright green leaves have three (sometimes
five) round to ovate, diversely lobed or toothed leaflets that usually
resemble oak leaves [45,62].  Small flowers occur in leaf axils, with
male and female flowers on separate plants [38,53].  The fruits are
white drupes [45].  Rhizomes are at or just below the soil surface, and
are extensive [46].
  • 7.  Bolsinger, Charles L. 1989. Shrubs of California's chaparral,        timberland, and woodland: area, ownership, and stand characteristics.        Res. Bull. PNW-RB-160. Portland, OR: U.S. Department of Agriculture,        Forest Service, Pacific Northwest Experiment Station. 50 p.  [7426]
  • 22.  Gartner, Barbara L. 1991. Relative growth rates of vines and shrubs of        western poison oak, Toxicodendron diversilobum (Anacardiaceae). American        Journal of Botany. 78(10): 1345-1353.  [16703]
  • 38.  Kingsbury, John M. 1964. Poisonous plants of the United States and        Canada. Englewood Cliffs, NJ: Prentice-Hall, Inc. 626 p.  [122]
  • 45.  Munz, Philip A. 1974. A flora of southern California. Berkeley, CA:        University of California Press. 1086 p.  [4924]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]
  • 62.  U.S. Department of Agriculture, Forest Service. 1937. Range plant        handbook. Washington, DC. 532 p.  [2387]

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Ecology

Habitat

Key Plant Community Associations

More info for the terms: association, shrub

Pacific poison-oak occurs in mixed evergreen forests [29,30,32,59], woodlands,
chaparral, [25,26,27], coastal sage scrub [39], and riparian zones
[25,26,27,39,58].  It is the most widespread shrub in California [7].
Holland [33] described a Pacific poison-oak chaparral community type that may be
maintained by frequent fire.  Because it is dominated by Pacific poison-oak,
little is known of its community composition.

Many of the plant species commonly associated with Pacific poison-oak were
previously listed under DISTRIBUTION AND OCCURRENCE information.  Other
common associates follow, listed by community type.

Associates in mixed evergreen forests include Pacific madrone (Arbutus
menziesii), sugar pine (Pinus lambertiana), bigleaf maple (Acer
macrophyllum), tanoak (Lithocarpus densiflorus), California bay
(Umbellularia californica), and chinquapin (Chrysolepsis chrysophylla)
[11,17,18,43].

Woodland associates include valley oak (Quercus lobata), interior live
oak (Q. wislizenii), Monterey pine (Pinus radiata) [42], Coulter pine
(P. coulteri) [9], bigcone Douglas-fir (Pseudotsuga macrocarpa) [8,64],
and California walnut (Juglans californica) [48].

Chaparral associates include toyon (Heteromeles arbutifolia), chamise
(Adenostoma fasciculatum), and California scrub oak (Quercus dumosa).
Coastal sage scrub associates include California sagebrush (Artemisia
californica), coyote brush (Baccharis pilularis), and sugar sumac (Rhus
ovata) [6,26,27,47,65].

Pacific poison-oak associates in riparian zones include bigleaf maple,
California sycamore (Plantus racemosa), white alder (Alnus rhombifolia),
[17], boxelder (Acer negundo), willow (Salix spp.), California
blackberry (Rubus vitifolius), toyon, and wild grape (Vitis spp.)  [69].

Published classifications naming Pacific poison-oak as a dominant part of the
vegetation are:

Description and classification of the forests of the upper Illinois
   River drainage of southwestern Oregon [1]
Preliminary plant associations of the Siskiyou Mountain Province [2]
Coast redwood ecological types of southern Monterey County, California [10]
Plant communities of Santa Rosa Island, Channel Islands National Park [14]
Plant association and management guide: Siuslaw National Forest [29]
Plant association and management guide: Willamette National Forest [30]
The community composition of California coastal sage scrub [39]
Plant associations within the Interior Valleys of the Umpqua River
   Basin, Oregon [55]
The vascular plant communities of California [59]
An introduction to the plant communities of the Santa Ana and San
   Jacinto Mountains [65].
  • 1.  Atzet, Thomas. 1979. Description and classification of the forests of        the upper Illinois River drainage of southwestern Oregon. Corvallis, OR:        Oregon State University. 211 p. Dissertation.  [6452]
  • 2.  Atzet, Thomas; Wheeler, David L. 1984. Preliminary plant associations of        the Siskiyou Mountain Province. Portland, OR: U.S. Department of        Agriculture, Forest Service, Pacific Northwest Region. 278 p.  [9351]
  • 6.  Biswell, H. H. 1961. Manipulation of chamise brush for deer range        improvement. California Fish and Game. 47(2): 125-144.  [6366]
  • 7.  Bolsinger, Charles L. 1989. Shrubs of California's chaparral,        timberland, and woodland: area, ownership, and stand characteristics.        Res. Bull. PNW-RB-160. Portland, OR: U.S. Department of Agriculture,        Forest Service, Pacific Northwest Experiment Station. 50 p.  [7426]
  • 8.  Bolton, Robert B., Jr.; Vogl, Richard J. 1969. Ecological requirements        of Pseudotsuga macrocarpa in the Santa Ana Mountains, California.        Journal of Forestry. 67: 112-116.  [10807]
  • 9.  Borchert, Mark. 1985. Serotiny and cone-habit variation in populations        of Pinus coulteri (Pinaceae) in the southern Coast Ranges of California.        Madrono. 32(1): 29-48.  [5997]
  • 10.  Borchert, Mark; Segotta, Daniel; Purser, Michael D. 1988. Coast redwood        ecological types of southern Monterey County, California. Gen. Tech.        Rep. PSW-107. Berkeley, CA: U.S. Department of Agriculture, Forest        Service, Pacific Southwest Forest and Range Experiment Station. 27 p.        [10225]
  • 11.  Bowler, Peter A. 1990. Riparian woodland: an endangered habitat in        southern California. In: Schoenherr, Allan A., ed. Endangered plant        communities of southern California: Proceedings, 15th annual symposium;        1989 October 28; Fullerton, CA. Special Publication No. 3. Claremont,        CA: Southern California Botanists: 80-97.  [21321]
  • 14.  Clark, Ronilee A.; Halvorson, William L.; Sawdo, Andell A.; Danielsen,        Karen C. 1990. Plant communities of Santa Rosa Island, Channel Islands        National Park. Tech. Rep. No. 42. Davis, CA: University of California at        Davis, Institute of Ecology, Cooperative National Park Resources Studies        Unit. 93 p.  [18246]
  • 17.  Davis, Frank W.; Hickson, Diana E.; Odion, Dennis C. 1988. Composition        of maritime chaparral related to fire history and soil, Burton Mesa,        Santa Barbara County, California. Madrono. 35(3): 169-195.  [6162]
  • 18.  Davis, Frank W.; Keller, Edward A.; Parikh, Anuja; Florsheim, Joan.        1989. Recovery of the chaparral riparian zone after wildfire. In:        Protection, management, and restoration for the 1990's: Proceedings of        the California riparian systems conference; 1988 September 22-24; Davis,        CA. Gen. Tech. Rep. PSW-110. Berkeley, CA: U.S. Department of        Agriculture, Forest Service, Pacific Southwest Forest and Range        Experiment Station: 194-203.  [13883]
  • 25.  Gray, M. Violet; Greaves, James M. 1984. Riparian forest as habitat for        the least Bell's vireo. In: Warner, Richard E.; Hendrix, Kathleen M.,        eds. California riparian systems: Ecology, conservation, and productive        management: Proceedings of a conference; 1981 September 17-19; Davis,        CA. Berkeley, CA: University of California Press: 605-611.  [5862]
  • 26.  Hanes, Ted L. 1976. Vegetation types of the San Gabriel Mountians. In:        Latting, June, ed. Symposium proceedings: plant communities of southern        California; 1974 May 4; Fullerton, CA. Special Publication No. 2.        Berkeley, CA: California Native Plant Society: 65-76.  [4227]
  • 27.  Hanes, Ted L. 1977. California chaparral. In: Barbour, Michael G.;        Major, Jack, eds. Terrestrial vegetation of California. New York: John        Wiley and Sons: 417-469.  [7216]
  • 29.  Hemstrom, Miles A.; Logan, Sheila E. 1986. Plant association and        management guide: Siuslaw National Forest. R6-Ecol 220-1986a. Portland,        OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest        Region. 121 p.  [10321]
  • 30.  Hemstrom, Miles A.; Logan, Sheila E.; Pavlat, Warren. 1987. Plant        association and management guide: Willamette National Forest. R6-Ecol        257-B-86. Portland, OR: U.S. Department of Agriculture, Forest Service,        Pacific Northwest Region. 312 p.  [13402]
  • 32.  Hitchcock, C. Leo; Cronquist, Arthur. 1973. Flora of the Pacific        Northwest. Seattle, WA: University of Washington Press. 730 p.  [1168]
  • 33.  Holland, Robert F. 1986. Preliminary descriptions of the terrestrial        natural communities of California. Sacramento, CA: California Department        of Fish and Game. 156 p.  [12756]
  • 39.  Kirkpatrick, J. B.; Hutchinson, C. F. 1977. The community composition of        Californian coastal sage scrub. Vegetatio. 35(1): 21-33.  [5612]
  • 42.  McDonald, Philip M.; Laacke, Robert J. 1990. Pinus radiata D. Don        Monterey pine. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 433-441.  [13401]
  • 43.  McKee, Arthur. 1990. Castanopsis chrysophylla (Dougl.) A. DC.  giant        chinkapin. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Vol. 2. Hardwoods. Agric. Handb.        654. Washington, DC: U.S. Department of Agriculture, Forest Service:        234-239.  [13962]
  • 47.  Pase, Charles P. 1982. Californian (coastal) chaparral. In: Brown, David        E., ed.  Biotic communities of the American Southwest--United States and        Mexico. Desert Plants. 4(1-4): 91-94.  [8891]
  • 48.  Quinn, Ronald D. 1990. The status of walnut forests and woodlands        (Juglans californica) in southern California. In: Schoenherr, Allan A.,        ed. Endangered plant communities of southern California: Proceedings,        15th annual symposium; 1989 October 28; Fullerton, CA. Special        Publication No. 3. Claremont, CA: Southern California Botanists: 42-54.        [21319]
  • 55.  Smith, Winston Paul. 1985. Plant associations within the interior        valleys of the Umpqua River Basin, Oregon. Journal of Range Management.        38(6): 526-530.  [2179]
  • 58.  Thilenius, John F. 1968. The Quercus garryana forests of the Willamette        Valley, Oregon. Ecology. 49(6): 1124-1133.  [8765]
  • 59.  Thorne, Robert F. 1976. The vascular plant communities of California.        In: Latting, June, ed. Symposium proceedings: plant communities of        southern California; 1974 May 4; Fullerton, CA. Special Publication No.        2. Berkeley, CA: California Native Plant Society: 1-31.  [3289]
  • 64.  Vogl, Richard J. 1973. Ecology of knobcone pine in the Santa Ana        Mountains, California. Ecological Monographs. 43: 125-143.  [4815]
  • 65.  Vogl, Richard J. 1976. An introduction to the plant communities of the        Santa Ana and San Jacinto Mountains. In: Latting, June, ed. Symposium        proceedings: plant communities of southern California; 1974 May 4;        Fullerton, CA. Special Publication No. 2. Berkeley, CA: California        Native Plant Society: 77-98.  [4230]
  • 69.  Zembal, Richard. 1990. Riparian habitat and breeding birds along the        Santa Margarita and Santa Ana Rivers of southern California. In:        Schoenherr, Allan A., ed. Endangered plant communities of southern        California: Proceedings, 15th annual symposium; 1989 October 28;        Fullerton, CA. Special Publication No. 3. Claremont, CA: Southern        California Botanists: 98-114.  [21322]

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Habitat: Plant Associations

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the term: shrub

   K001  Spruce - cedar - hemlock forest
   K002  Cedar - hemlock - Douglas-fir forest
   K005  Mixed conifer forest
   K006  Redwood forest
   K009  Pine - cypress forest
   K010  Ponderosa shrub forest
   K026  Oregon oakwoods
   K028  Mosaic of K002 and K026
   K029  California mixed evergreen forest
   K030  California oakwoods
   K033  Chaparral
   K034  Montane chaparral
   K035  Coastal sagebrush

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Habitat: Ecosystem

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

   FRES20  Douglas-fir
   FRES21  Ponderosa pine
   FRES24  Hemlock - Sitka spruce
   FRES27  Redwood
   FRES28  Western hardwoods
   FRES34  Chaparral - mountain shrub

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Habitat characteristics

Pacific poison-oak generally grows in acid soils, and is not limited to any
particular soil texture or drainage pattern.  It occurs on well-drained
slopes and in riparian zones [1,39,64].  It is found at elevations of
less than 5,000 feet (1,524 m) west of the Sierra Nevada, growing on all
aspects [45].  In the Siskiyou Mountains it is found at up to 4,400-foot
(1,340-m) elevations on steep southern exposures [66].
  • 1.  Atzet, Thomas. 1979. Description and classification of the forests of        the upper Illinois River drainage of southwestern Oregon. Corvallis, OR:        Oregon State University. 211 p. Dissertation.  [6452]
  • 39.  Kirkpatrick, J. B.; Hutchinson, C. F. 1977. The community composition of        Californian coastal sage scrub. Vegetatio. 35(1): 21-33.  [5612]
  • 45.  Munz, Philip A. 1974. A flora of southern California. Berkeley, CA:        University of California Press. 1086 p.  [4924]
  • 64.  Vogl, Richard J. 1973. Ecology of knobcone pine in the Santa Ana        Mountains, California. Ecological Monographs. 43: 125-143.  [4815]
  • 66.  Waring, R. H. 1969. Forest plants of the eastern Siskiyous: their        environment and vegetational distribution. Northwest Science. 43(1):        1-17.  [9047]

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Habitat: Cover Types

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

   213  Grand fir
   222  Black cottonwood - willow
   224  Western hemlock
   229  Pacific Douglas-fir
   230  Douglas-fir - western hemlock
   231  Port Orford-cedar
   232  Redwood
   233  Oregon white oak
   234  Douglas-fir - tanoak - Pacific madrone
   235  Cottonwood - willow
   243  Sierra Nevada mixed conifer
   244  Pacific ponderosa pine - Douglas-fir
   245  Pacific ponderosa pine
   246  California black oak
   247  Jeffrey pine
   248  Knobcone pine
   249  Canyon live oak
   250  Blue oak - Digger pine
   255  California coast live oak

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General Ecology

Fire Management Considerations

More info for the terms: cover, fuel, fuel continuity, prescribed fire, shrub, vines

Urushiol volatilizes when burned, and human exposure to Pacific poison-oak smoke
is extremely hazardous [40].  The smoke often poisons people who think
they are immune to the plant [46].

Pacific poison-oak vines are a ladder fuel [61].

Goats can be used as an alternative to prescribed fire for fire hazard
reduction at urban-wildland interfaces.  Near Oakland, California, goats
were put on a Monterey pine-redgum (Eucalyptus camaldensis) forest with
a heavy shrub understory and on an adjacent site where the forest was
managed as a fuelbreak and had less shrub cover in the understory.  Goat
utilization of Pacific poison-oak was in the fuelbreak 67 percent, somewhat
lower than utilization of toyon, California blackberry, and coyote brush.
Annual production of Pacific poison-oak biomass before goat browsing in the
fuelbreak was 99 kilograms per hectare; it was 33 kilograms per hectare
afterwards.  Total biomass of forage species was significantly (p less than 0.05)
reduced [61].

A stocking rate of 600 goats per hectare on the Oakland site broke the
vertical live fuel continuity in the dense shrub stand.  Initial goat
browsing to reduce biomass and vertical fuel continuity could be
followed up by prescribed fire [61].
  • 40.  Kouakou, Brou; Rampersad, David; Rodriguez, Eloy; Brown, Dan L. 1992.        Dairy goats used to clear poison oak do not transfer toxicant to milk.        California Agriculture. 46(3): 4-6.  [19691]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]
  • 61.  Tsiouvaras, C. N.; Havlik, N. A.; Bartolome, J. W. 1989. Effects of        goats on understory vegetation and fire hazard reduction in coastal        forest in California. Forest Science. 35(4): 1125-1131.  [9767]

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Broad-scale Impacts of Plant Response to Fire

Fire response is probably related to Poison oak's successional role in
the plant community.  Dense Pacific poison-oak thickets may develop in chaparral
that is control burned several times [12].  Pacific poison-oak may become
locally extinct in Douglas-fir forest, however, that is burned every 4
years for 20 years or more [53].
  • 12.  Burcham, L. T. 1974. Fire and chaparral before European settlement. In:        Rosenthal, Murray, ed. Symposium on living with the chaparral:        Proceedings; 1973 March 30-31; Riverside, CA. San Francisco, CA: The        Sierra Club: 101-120.  [4669]
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]

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Plant Response to Fire

More info for the terms: backfire, density, fire use, prescribed fire, root crown, wildfire

Pacific poison-oak sprouts vigorously from the root crown and/or rhizomes after
fire [13,15,43,46,52].  It sprouts in the first postfire growing season,
and for several years thereafter [13,16,52].  Pacific poison-oak sprouts were
noted the September following the July, 1985, Wheeler Fire on the Los
Padres National Forest, California.  The wildfire had spread into a
riparian zone containing Pacific poison-oak; prefire Pacific poison-oak density was
unknown.  By postfire year 3, Pacific poison-oak sprouts dominated most burn
plots in the riparian zone [18].

Westman and others [67] estimated that Pacific poison-oak fails to sprout when
fire reaction intensity exceeds 200 kcal/sec/sq m.  Their estimate was
derived by modelling fire behavior of a backfire set in coastal sage
scrub in the Santa Monica Mountains of California, and observing
sprouting the following year.  The coastal sage scrub had not burned for
20 to 22 years.

Pacific poison-oak also establishes from seed after fire, although this response
is not well documented in the literature.  Pacific poison-oak seedlings were
observed following site preparation and prescribed burning of an
interior live oak-blue oak woodland in Madera County, California.
Prefire Pacific poison-oak seedling density was 0 percent; seedling density at
postfire year 1 was 42 per 8,712 square feet [20].
Response of vegetation to prescribed burning in a Jeffrey pine-California
black oak woodland and a deergrass meadow at Cuyamaca State Park,
California
provides information on prescribed fire use and postfire
response of many mixed-conifer woodland species including Pacific poison-oak.
  • 13.  Christensen, Norman L.; Muller, Cornelius H. 1975. Effects of fire on        factors controlling plant growth in Adenostoma chaparral. Ecological        Monographs. 45: 29-55.  [4923]
  • 15.  Conrad, C. Eugene. 1987. Common shrubs of chaparral and associated        ecosystems of southern California. Gen. Tech. Rep. PSW-99. Berkeley, CA:        U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest        and Range Experiment Station. 86 p.  [4209]
  • 16.  Cook, Sherburne F., Jr. 1959. The effects of fire on a population of        small rodents. Ecology. 40(1): 102-108.  [230]
  • 18.  Davis, Frank W.; Keller, Edward A.; Parikh, Anuja; Florsheim, Joan.        1989. Recovery of the chaparral riparian zone after wildfire. In:        Protection, management, and restoration for the 1990's: Proceedings of        the California riparian systems conference; 1988 September 22-24; Davis,        CA. Gen. Tech. Rep. PSW-110. Berkeley, CA: U.S. Department of        Agriculture, Forest Service, Pacific Southwest Forest and Range        Experiment Station: 194-203.  [13883]
  • 20.  Frost, William E. 1989. The Ellis Ranch project: a case study in        controlled burning. No. 891002. Fresno, CA: California Agricultural        Technology Institute and the San Joaquin Experimental Range. 11 p.        [13817]
  • 43.  McKee, Arthur. 1990. Castanopsis chrysophylla (Dougl.) A. DC.  giant        chinkapin. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Vol. 2. Hardwoods. Agric. Handb.        654. Washington, DC: U.S. Department of Agriculture, Forest Service:        234-239.  [13962]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]
  • 52.  Sampson, Arthur W. 1944. Effect of chaparral burning on soil erosion and        on soil-moisture relations. Ecology. 25(2): 171-191.  [16841]
  • 67.  Westman, W. E.; O'Leary, J. F.; Malanson, G. P. 1981. The effects of        fire intensity, aspect and substrate on post-fire growth of Californian        coastal sage scrub. In: Margaris, N. S.; Mooney, H. A., eds. Components        of productivity of Mediterranean climate regions--basic and applied        aspects. The Hague, Netherlands: Dr W. Junk Pulishers: 151-179.  [13593]

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Immediate Effect of Fire

More info for the term: wildfire

Fire top-kills Pacific poison-oak [13,16].  Wirtz [68] reported that an October,
1953, wildfire in a coastal sage scrub/grassland community near
Berkeley, California, top-killed all Pacific poison-oak present, leaving only
large branches and stumps.

Rhizomes on the soil surface are probably killed by all but
light-severity fire, and shallowly buried rhizomes are probably killed
by moderate to severe fire.  More deeply buried rhizomes are probably
not killed.
  • 13.  Christensen, Norman L.; Muller, Cornelius H. 1975. Effects of fire on        factors controlling plant growth in Adenostoma chaparral. Ecological        Monographs. 45: 29-55.  [4923]
  • 16.  Cook, Sherburne F., Jr. 1959. The effects of fire on a population of        small rodents. Ecology. 40(1): 102-108.  [230]
  • 68.  Wirtz, W. O., II. 1982. Postfire community structure of birds and        rodents in southern California chaparral. In: Conrad, C. Eugene; Oechel,        Walter C., technical coordinators. Proceedings of the symposium on        dynamics and management of Mediterranean-type ecosystems; 1981 June        22-26; San Diego, CA. Gen. Tech. Rep. PSW-58. Berkeley, CA: U.S.        Department of Agriculture, Forest Service, Pacific Southwest Forest and        Range Experiment Station: 241-246.  [6025]

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Post-fire Regeneration

More info for the terms: ground residual colonizer, rhizome, secondary colonizer, shrub

   Tall shrub, adventitious-bud root crown
   Rhizomatous shrub, rhizome in soil
   Ground residual colonizer (on-site, initial community)
   Secondary colonizer - off-site seed

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Fire Ecology

More info for the terms: charate, fresh, root crown

Pacific poison-oak's primary POSTFIRE REGENERATION STRATEGY is vigorous
sprouting from the root crown and/or rhizomes [16,46,68].

Fire is not required for Pacific poison-oak seed germination.  Keeley [37],
however, reported a significant (p less than 0.001) increase in germination when
seeds were exposed to charate.  Postfire seedlings probably originate
from both soil-stored seed and fresh seed dispersed by birds.
  • 16.  Cook, Sherburne F., Jr. 1959. The effects of fire on a population of        small rodents. Ecology. 40(1): 102-108.  [230]
  • 37.  Keeley, Jon E. 1987. Role of fire in seed germination of woody taxa in        California chaparral. Ecology. 68(2): 434-443.  [5403]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]
  • 68.  Wirtz, W. O., II. 1982. Postfire community structure of birds and        rodents in southern California chaparral. In: Conrad, C. Eugene; Oechel,        Walter C., technical coordinators. Proceedings of the symposium on        dynamics and management of Mediterranean-type ecosystems; 1981 June        22-26; San Diego, CA. Gen. Tech. Rep. PSW-58. Berkeley, CA: U.S.        Department of Agriculture, Forest Service, Pacific Southwest Forest and        Range Experiment Station: 241-246.  [6025]

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Successional Status

More info on this topic.

More info for the terms: climax, cover

Facultative Seral Species

Pacific poison-oak is a somewhat shade-tolerant species commonly occurring in
seral woodland and mixed evergreen forest understories [51,56].  It is
considered a climax species on south-slope Douglas-fir forests of the
Willamette Valley foothills, Oregon [51].  In climax oak woodland,
Pacific poison-oak cover may reach 25 to 50 percent [17].
  • 17.  Davis, Frank W.; Hickson, Diana E.; Odion, Dennis C. 1988. Composition        of maritime chaparral related to fire history and soil, Burton Mesa,        Santa Barbara County, California. Madrono. 35(3): 169-195.  [6162]
  • 51.  Sabhasri, Sanga ; Ferrell, William K. 1960. Invasion of brush species        into small stand openings in the Douglas-fir forests of the Willamette        Foothills. Northwest Science. 34(3): 77-89.  [8652]
  • 56.  Stein, William I. 1980. Oregon white oak. In: Eyre, F. H. ., ed. Forest        cover types of the United States and Canada. Washington, DC: Society of        American Foresters: 110-111.  [9857]

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Regeneration Processes

More info for the terms: layering, vine

Pacific poison-oak reproduces vegetatively by sprouting from the rhizomes and
root crown after disturbance such as fire or browsing has removed
topgrowth [15,44,53].  It also reproduces by layering when vine stems
contact the ground [46].

Pacific poison-oak seeds are dispersed by birds [53].  Seedlings occur both
before and after fire, suggesting that the seeds do not depend upon fire
for scarification.  The seeds have a gummy seedcoat which leaches off
very slowly, resulting in delayed germination [37].

Pacific poison-oak is propagated by stem cuttings [23].
  • 15.  Conrad, C. Eugene. 1987. Common shrubs of chaparral and associated        ecosystems of southern California. Gen. Tech. Rep. PSW-99. Berkeley, CA:        U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest        and Range Experiment Station. 86 p.  [4209]
  • 23.  Gartner, Barbara L; Thomas, Donald E. 1988. Vegetative propagation of        poison oak (California). Restoration & Management Notes. 6(1): 48-49.        [5474]
  • 37.  Keeley, Jon E. 1987. Role of fire in seed germination of woody taxa in        California chaparral. Ecology. 68(2): 434-443.  [5403]
  • 44.  McKell, Cyrus M.; Blaisdell, James P.; Goodin, Joe R., eds. 1972.        Wildland shrubs--their biology and utilization: An international        symposium; 1971 July; Logan, UT. Gen. Tech. Rep. INT-1. Ogden, UT: U.S.        Department of Agriculture, Forest Service, Intermountain Forest and        Range Experiment Station. 494 p.  [1612]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]

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Growth Form (according to Raunkiær Life-form classification)

More info on this topic.

More info for the terms: hemicryptophyte, phanerophyte

   Phanerophyte
   Hemicryptophyte

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Life Form

More info for the terms: shrub, vine

Vine, Shrub

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Life History and Behavior

Cyclicity

Phenology

More info on this topic.

Pacific poison-oak leaf buds open from February to March, and stems elongate
from March to April [37].  Flowering occurs from March to
June [15].  Leaves drop from late July to early October [22],
and fruits disperse in summer and fall [37,53].
  • 15.  Conrad, C. Eugene. 1987. Common shrubs of chaparral and associated        ecosystems of southern California. Gen. Tech. Rep. PSW-99. Berkeley, CA:        U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest        and Range Experiment Station. 86 p.  [4209]
  • 22.  Gartner, Barbara L. 1991. Relative growth rates of vines and shrubs of        western poison oak, Toxicodendron diversilobum (Anacardiaceae). American        Journal of Botany. 78(10): 1345-1353.  [16703]
  • 37.  Keeley, Jon E. 1987. Role of fire in seed germination of woody taxa in        California chaparral. Ecology. 68(2): 434-443.  [5403]
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]

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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: N2 - Imperiled

United States

Rounded National Status Rank: N5 - Secure

Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

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Source: NatureServe

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Management

Management considerations

More info for the terms: fire management, vines

Safety/Medical:  The entire Pacific poison-oak plant is covered with oily resin.
Human dermatitis results when skin comes in direct contact with the oil,
either by touching the plant or touching something that has contacted
it, such as clothing or firewood.  Urushiol is the poison present in the
oil [46].  Pacific poison-oak does not cause dermatitis in wildlife or
livestock, but pets may react to it [53]. (See FIRE MANAGEMENT.) American
folklore holds that drinking the milk of Pacific poison-oak-fed goats bolsters
the immune system against Pacific poison-oak because the poison is present in
the milk in trace amounts.  Drinking the milk probably does not grant
immunity, however.  Analysis of milk from does fed a straight Pacific poison-oak
diet for 3 days showed no trace of urushiol.  Some urushiol was present
in the does' urine, but most was apparently catabolized [40].

Control:  Pacific poison-oak is controlled by glyphosate, triclopyr, or 2,4,5-T.
Used alone, 2,4-D is ineffective.  Goats are an effective biological
control [40,50].

Other:  Pacific poison-oak vines sometimes kill their support plant by
smothering or breaking it [46].

Pacific poison-oak blossoms are a source of good honey [46].
  • 40.  Kouakou, Brou; Rampersad, David; Rodriguez, Eloy; Brown, Dan L. 1992.        Dairy goats used to clear poison oak do not transfer toxicant to milk.        California Agriculture. 46(3): 4-6.  [19691]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]
  • 50.  Rice, Carol. 1990. Restoration plays an integral role in fire hazard        reduction plan for the Berkeley Hills Area. Restoration & Management        Notes. 8(2): 125-126.  [13792]
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]

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Relevance to Humans and Ecosystems

Benefits

Value for rehabilitation of disturbed sites

More info for the term: restoration

Pacific poison-oak has been recommended for use in restoration projects.
Information on propagation and handling methods to "minimize risks" to
planting crews is available [23].  Having worked on field crews in the
Sierra Nevada foothills, however, this author recommends using native
shrubs other than Pacific poison-oak for restoration.
  • 23.  Gartner, Barbara L; Thomas, Donald E. 1988. Vegetative propagation of        poison oak (California). Restoration & Management Notes. 6(1): 48-49.        [5474]

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Cover Value

More info for the term: density

The federally endangered least Bell's vireo uses Pacific poison-oak for nest
sites in oak woodlands [25]. 

Fremont cottonwood (Populus fremontii)/Pacific poison-oak woodlands contribute
to bird diversity and density in California [28].  A rare colony of
ringtail was found inhabiting a Fremont cottonwood/Pacific poison-oak woodland
on the Sacramento River [3].
  • 3.  Belluomini, Linda; Trapp, Gene R. 1984. Ringtail distribution and        abundance in the Central Valley of California. In: Warner, Richard E.;        Hendrix, Kathleen M., eds. California riparian systems: Ecology,        conservation, and productive management. Berkeley, CA: University of        California Press: 906-914.  [5880]
  • 25.  Gray, M. Violet; Greaves, James M. 1984. Riparian forest as habitat for        the least Bell's vireo. In: Warner, Richard E.; Hendrix, Kathleen M.,        eds. California riparian systems: Ecology, conservation, and productive        management: Proceedings of a conference; 1981 September 17-19; Davis,        CA. Berkeley, CA: University of California Press: 605-611.  [5862]
  • 28.  Hehnke, Merlin; Stone, Charles P. 1979. Value of riparian vegetation to        avian populations along the Sacramento River Sy. In: Johnson, R. Roy;        McCormick, J. Frank, technical coordinators. Strategies for protection        and management of floodplain wetlands & other riparian ecosystems: Proc.        of the symposium; 1978 December 11-13; Callaway Gardens, GA. General        Technical Report WO-12. Washington, DC: U.S. Department of Agriculture,        Forest Service: 228-235.  [4363]

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Nutritional Value

Percent crude protein in Pacific poison-oak foliage collected throughout
California averaged 24.2 in March, 20.6 in May, 10.1 in July, and 6.5 in
September [5].  Pacific poison-oak is relatively high in phosphorus, sulfur,
and calcium as compared to other browse species [24].  The following
mineral content (percentage basis) was reported for the foliage [54]:

                   Ca     P     K     Mg     S
                 1.00   0.23  1.13  0.59   0.19
  • 5.  Bissell, Harold D.; Strong, Helen. 1955. The crude protein variations in        the browse diet of California deer. California Fish and Game. 41(2):        145-155.  [10524]
  • 24.  Gordon, Aaron; Sampson, Arthur W. 1939. Composition of common California        foothill plants as a factor in range management. Bull. 627. Berkeley,        CA: University of California, College of Agriculture, Agricultural        Experiment Station. 95 p.  [3864]
  • 54.  Scrivner, Jerry H.; Vaughn, Charles E.; Jones, Milton B. 1988. Mineral        concentrations of black-tailed deer diets in California chaparral.        Journal of Wildlife Management. 52(1): 37-40.  [3055]

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Other uses and values

Urushiol has been found to mediate DNA strand scission.  This activity
may have application in DNA sequence studies [70].

Native Americans used the stems to make baskets and the sap to cure
ringworm [15,60].  Chumash Indians used Pacific poison-oak sap to remove warts,
corns, and calluses; to cauterize sores; and to stop bleeding.  They
drank a decoction made from Pacific poison-oak roots to treat dysentery [60].
  • 15.  Conrad, C. Eugene. 1987. Common shrubs of chaparral and associated        ecosystems of southern California. Gen. Tech. Rep. PSW-99. Berkeley, CA:        U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest        and Range Experiment Station. 86 p.  [4209]
  • 60.  Timbrook, Jan. 1990. Ethnobotany of Chumash Indians, California, based        on collections by John P. Harrington. Economic Botany. 44(2): 236-253.        [13777]
  • 70.  Wasser, Charles; Silva, F.; Rodriquez, E. 1990. Urushiol components as        mediators in DNA strand scission. Experientia. 46(5): 500-502.  [22399]

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Importance to Livestock and Wildlife

Black-tailed deer and all classes of livestock browse Pacific poison-oak [53].
It is the most important black-tailed deer browse in some areas of
California [5,6].  Birds eat Pacific poison-oak fruits [53].
  • 5.  Bissell, Harold D.; Strong, Helen. 1955. The crude protein variations in        the browse diet of California deer. California Fish and Game. 41(2):        145-155.  [10524]
  • 6.  Biswell, H. H. 1961. Manipulation of chamise brush for deer range        improvement. California Fish and Game. 47(2): 125-144.  [6366]
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]

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Palatability

Pacific poison-oak palatability is rated good to fair for horses and deer; and
fair to poor for cattle, sheep, and goats [53].
  • 53.  Sampson, Arthur W.; Jespersen, Beryl S. 1963. California range        brushlands and browse plants. Berkeley, CA: University of California,        Division of Agricultural Sciences, California Agricultural Experiment        Station, Extension Service. 162 p.  [3240]

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Wikipedia

Toxicodendron diversilobum

Toxicodendron diversilobum, commonly named Pacific poison oak or western poison oak (syn. Rhus diversiloba), is a woody vine or shrub in the Anacardiaceae (sumac) family. It is widely distributed in western North America, inhabiting conifer and mixed broadleaf forests, woodlands, grasslands, and chaparral biomes.[1] It is known for causing itching and allergic rashes in many humans, after contact by touch or smoke inhalation.

Distribution[edit]

T. diversilobum is found in California (also the original name of Los Angeles; Yangna or Iyaanga/poison oak place),[2] the Baja California peninsula, Nevada, Oregon, Washington, and British Columbia.[3] The related T. pubescens (eastern poison oak) is native to the Southeastern United States. T. diversilobum and T. rydbergii (western poison ivy) hybridize in the Columbia River Gorge area.[4]

T. diversilobum is common in various habitats, from mesic riparian zones to xeric chaparral.[5] It thrives in shady and dappled light through full and direct sunlight conditions, at elevations below 5,000 feet (1,500 m).[4] 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.[4]

The plant often occurs in chaparral and woodlands, coastal sage scrub, grasslands, and oak woodlands; and Douglas-fir (Pseudotsuga menzesii), hemlock–Sitka spruce, Sequoia sempervirens (coast redwood), Pinus ponderosa (Ponderosa pine), and mixed evergreen forests.[6]

Description[edit]

T. diversilobum is extremely variable in growth habit and leaf appearance. It grows as a dense 0.5–4 m (1.6–13.1 ft) tall shrub in open sunlight, a treelike vine 10–30 feet (3.0–9.1 m) and may be more than more than 100 feet (30 m) long with an 8–20 cm (3.1–7.9 in) trunk, as dense thickets in shaded areas, or any form in between [4][7] It reproduces by spreading rhizomes and by seeds.[1]

The plant is winter deciduous, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of berries. 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, 3.5 to 10 centimetres (1.4 to 3.9 in) long, with scalloped, toothed, or lobed edges.[5] 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.[4]

White flowers form in the spring, from March to June.[4] If they are fertilized, they develop into greenish-white or tan berries.[5]

Botanist John Howell observed the toxicity of T. diversilobum 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."[8]

Toxin qualities[edit]

T. diversilobum leaves and twigs have a surface oil, urushiol, which causes an allergic reaction.[1] It causes contact dermatitis – an immune-mediated skin inflammation – in four-fifths of humans.[9][10] However, 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 by to be unsaturated congeners of 3-heptadecylcatechol with up to three double bonds in an unbranched C17 side chain.[11] In poison ivy, these components are unique in that they contain a -CH2CH2- group in an unbranched alkyl side chain.[12]

Reactions[edit]

T. diversilobum skin contact first causes itching; then evolves into dermatitis with inflammation, colorless bumps, severe itching, and blistering.[13] In the dormant deciduous seasons the plant can be difficult to recognize, however leafless branches and twigs contact also causes allergic reactions.

Urushiol volatilizes when burned, and human exposure to T. diversilobum smoke is extremely hazardous, from wildfires, controlled burns, or disposal fires.[4] The smoke can poison people who thought they were immune.[4] Branches used to toast food over campfires can cause reactions internally and externally.

Ecology[edit]

Black-tailed deer, mule deer, California ground squirrels, western gray squirrels, and other indigenous fauna feed on the leaves of the plant.[4] It is rich in phosphorus, calcium, and sulfur.[4] Bird species use the berries for food, and utilize the plant structure for shelter.[4] Neither native animals, nor horses, livestock, or canine pets demonstrate reactions to urushiol.[1]

Due to human allergic reactions, T. diversilobum is usually eradicated from gardens and public landscaped areas. It can be a weed in agricultural fields, orchards, and vineyards.[14] It is usually removed by pruning, herbicides, digging out, or a combination.[15]

Uses[edit]

Medicinal[edit]

Californian Native Americans used the plant's stems and shoots to make baskets, the sap to cure ringworm, and as a poultice of fresh leaves applied to rattlesnake bites.[16] The juice or soot was used as a black dye for sedge basket elements, tattoos, and skin darkening.[16][17]

An infusion of dried roots, or buds eaten in the spring, were taken by some native peoples for an immunity from the plant poisons.[16]

Chumash peoples used T. diversilobum sap to remove warts, corns, and calluses; to cauterize sores; and to stop bleeding.[16] They drank a decoction made from the roots to treat dysentery.[18]

Cultivation[edit]

T.diversilobum can be a carefully situated component in wildlife gardens, habitat gardens, and natural landscaping.

The plant is used in habitat restoration projects.[4] It can be early stage succession where woodlands have been burned or removed, serving as a nurse plant for other species.

See also[edit]

References[edit]

  1. ^ a b c d C. Michael Hogan (2008); "Western poison-oak: Toxicodendron diversilobum", GlobalTwitcher, ed. Nicklas Strömberg
  2. ^ Ron Sullivan (December 7, 2002). "Roots of native names"
  3. ^ "Toxicodendron diversilobum". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 2013-09-20. 
  4. ^ a b c d e f g h i j k l U.S. Forest Service: Toxicodendron diversilobum
  5. ^ a b c Jepson
  6. ^ Calflora
  7. ^ Integrated Taxonomic Information System (ITIS): Toxicodendron diversilobum (Western Poison-oak) - Overview
  8. ^ John Thomas Howell, Frank Almeda, Wilma Follette & Catherine Best (2007). Marin Flora. California Academy of Sciences; California Native Plant Society. p. 264. ISBN 094022870X. 
  9. ^ R. S. Kalish, J. A. Wood & A. LaPorte (1994). "Processing of urushiol (poison ivy) hapten by both endogenous and exogenous pathways for presentation to T cells in vitro". Journal of Clinical Investigation 93 (5): 2039–2047. doi:10.1172/jci117198. PMC 294319. PMID 7910172. 
  10. ^ Mic-ro.com: Contact-Poisonous Plants of the World
  11. ^ Michael D. Corbett & Stephen Billets (1975). "Characterization of poison oak urushiol". Journal of Pharmaceutical Sciences 64 (10): 1715–1718. doi:10.1002/jps.2600641032. 
  12. ^ John C. Craig, Coy W. Waller, Stephen Billets & Mahmoud A. Elsohly (1978). "New GLC analysis of urushiol congeners in different plant parts of poison ivy, Toxicodendron radicans". Journal of Pharmaceutical Sciences 67 (4): 483–485. doi:10.1002/jps.2600670411. 
  13. ^ Poison Oak/Poison Ivy Information Center
  14. ^ UC Integrated Pest Management Weed Photo Gallery and information (profile of this plant as an agricultural weed).
  15. ^ Sunset Western Garden Book [5th edition], (Menlo Park: Sunset Publishing, 1988), p. 506
  16. ^ a b c d Univ. of Michigan, Dearborn – Native American Ethnobotany Database: Toxicodendron diversilobum
  17. ^ Conrad, C. Eugene. 1987. "Common shrubs of chaparral and associated ecosystems of southern California". Gen. Tech. Rep. PSW-99. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 86 p.
  18. ^ Jan Timbrook (1990). "Ethnobotany of Chumash Indians, California, based on collections by John P. Harrington". Economic Botany 44 (2): 236–253. doi:10.1007/BF02860489. JSTOR 4255231. 

Gallery[edit]

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Names and Taxonomy

Taxonomy

Common Names

Pacific poison-oak
Pacific poison oak

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The currently accepted scientific name of Pacific poison-oak is Toxicodendron
diversilobum (Torr. & Gray) E. Greene (Anacardiacae) [31]. Pacific poison-oak
and western poison-ivy (Toxicodendron rydbergii) hybridize in the Columbia River
Gorge area [38].
  • 31.  Hickman, James C., ed. 1993. The Jepson manual: Higher plants of        California. Berkeley, CA: University of California Press. 1400 p.        [21992]
  • 38.  Kingsbury, John M. 1964. Poisonous plants of the United States and        Canada. Englewood Cliffs, NJ: Prentice-Hall, Inc. 626 p.  [122]

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Synonyms

Rhus diversiloba Torr. & A. Gray [46]
  • 46.  Pacific Northwest Extension Service. 1983. Poison oak and ivy. PNW 108.        Corvallis, OR; Pullman, WA; Moscow, ID. 2 p.  [6613]

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