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Toxicodendron diversilobumWestern Poison Oak
 
Toxicodendron diversilobum
Toxicodendron diversilobum Toxicodendron diversilobum Toxicodendron diversilobum Toxicodendron diversilobum
 

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Poison Oak is California's most prevalent wild shrub. It will form dense thickets, grow as a climbing vine, shrub or a small tree. Deserts, dense forests and altitudes above 4000-5000 feet are the only restraints to its growth. The common name refers to the striking similarity of the leaves to the genus Quercus (Oak).

The body's response to poison oak, or more specifically to the chemical compound, urushiol, is an allergic reaction. The body's immune system goes haywire and responds to the urushiol as a threat. The body then sets out to contain and destroy it. The resulting itchy, blistery rash can be miserable and in severe cases requires medical attention.

Urushiol is not a poison in the true sense of the word, like arsenic or strychnine. You won't get poison oak by merely being in its presence. You must touch the plant or another object that has been in contact with the plant, such as clothing, tools or the family pet. Urushiol is contained in the leaves, stems, roots and skin of the berries. Consequently, exposure can occur even when it has lost its leaves in the winter. It is particularly seductive in the autumn when the leaves turn a bright, beautiful red. The oil does not dry up and disappear with time. People have been exposed when handling centuries old dried specimens in herbariums. When it is burned, droplets can also be carried on smoke and soot particles, depositing it into the lungs.

About 10-15% of the population are truly not sensitive to urushiol. The other 85% are vulnerable to varying degrees, with 10-15% falling in the category of exquisitely sensitive. The actual degree of any given reaction depends on the amount of urushiol and an individual's sensitivity.

Poison oak has small white flowers and white berries, but the bright fall colors are what give this plant its biggest opportunity for identification. Other times of year, the old rule, "leaves of three let them be" is the best way to steer clear of this toxic plant.

Profile
Scientific Name Toxicodendron diversilobum
Family Anacardiaceae
Plant Type Variable: Vine, Shrub, Small Tree
Environment Grows well in sun or shade.
Bloom White flowers appear in spring
Uses Not recommended for planting. Native Americans used the stems to make baskets and the sap to cure ringworm. Chumash Indians used poison-oak sap to remove warts,corns, and calluses; to cauterize sores; and to stop bleeding. They drank a decoction made from poison-oak roots to treat dysentery.
More Info Poison Ivy (T. radicans) and Poison Sumac (T. vernix) contain the same chemical, urushiol, and can cause the same allergic reaction.

T. diversilobum is the most widespread shrub in California and has a range from Baja, California north to British Colombia

Poison oak does not cause a reaction in wildlife or livestock, but some pets may react to it.
Location

Toxicodendron diversilobum can be found in the California Native Garden (Bed 39B).

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IN BLOOM CONTRIBUTORS:
Photos by Docent Joanne Taylor
Text by Docent Kathy McNeil
Profile by Associate Curator David Kruse-Pickler

 
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Magnolia campbellii 'Strybing White'

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Magnolia laevifolia 'Strybing Compact'

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Montanoa spp.

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Acer palmatum 'Sango kaku'

Acer palmatum 'Sango kaku'

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Magnolia campbellii 'Darjeeling'

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Bomaria spp.

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Rhododendron occidentale

Rhododendron occidentale

April

Polystichum munitum

Polystichum munitum

May

x Chiranthofremontia lenzii

x Chiranthofremontia lenzii

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Wollemia nobilis

Wollemia nobilis

September

Cyathea cooperi

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Pinus radiata

Pinus radiata

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Correa spp.

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Garrya elliptica

Garrya elliptica

January

Magnolia x soulangeana

Magnolia x soulangeana

February

Senecio glastifolius

Senecio glastifolius

March

Ribes spp.

Ribes spp.

April

Oxalis oregana

Oxalis oregana

May

Calandrinia grandiflora

Calandrinia grandiflora

June

Taxus baccata

Taxus baccata

July

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Romneya coulteri

August

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Passiflora parritae

September

Malvaviscus arboreus

Malvaviscus arboreus

October

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Monterey Cypress

November

Aloe arborescens

Aloe arborescens

December

Aloe plicatilis

Aloe plicatilis

January

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Banksia seminuda

February

Zantedeschia elliottiana

Zantedeschia aethiopica

March

Magnolia laevifolia

Magnolia laevifolia

April

Araucaria heterophylla

Araucaria heterophylla

May

Toxicodendron diversilobum

Toxicodendron diversilobum

June

Clarkia sp.

Clarkia sp.

July

Agapanthus

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Brugmansia

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September

Cedrus spp.

Cedrus spp.

October

Protea repens

Protea repens

November

Camellia sinensis

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Thujopsis dolabrata

Thujopsis dolabrata

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Gordonia longicarpa

Gordonia longicarpa

February

Rojasianthe superba

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March

Echium spp.

Echium spp.

April

Iris douglasiana

Iris douglasiana

May

Digitalis purpurea

Digitalis purpurea

June

Felicia amelloides

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August

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October

Acer morrisonense

Acer morrisonense

November

Ilex aquifolium

Ilex aquifolium

December

Picea sitchensis

Picea sitchensis

January

Telanthophora grandifolia

Telanthophora grandifolia

February

Aeonium arboreum 'Schwartzkopf'

Aeonium arboreum 'Schwartzkopf'

March

Leptospermum Spp.

Leptospermum

April

Salvia gesneraeflora

Salvia gesneraeflora

May

Lavandula spp.

Lavandula spp.

June

Pelargonium

Pelargonium

July

Fuchsia paniculata

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August

Luma apiculata

Luma apiculata

September

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October

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Arbutus unedo

November

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December

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Restionaceae

January

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February

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March

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April

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Psoralea pinnata

May

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Fremontodendron californicum

June

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Leucadendron argenteum

July

Crocosmia

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Gunnera tinctoria

Gunnera tinctoria

September

Pellaea rotundifolia

Pellaea rotundifolia

October

Fuchsia boliviana

Fuchsia boliviana

November

Erica canaliculata

Erica canaliculata

December

Magnolia campbelli

Magnolia campbelli

January

Magnolia denudata

Magnolia denudata

February

Camellia

Camellia

March

Geranium maderense

Geranium maderense

April

Acmena smithii

Acmena smithii

May

Eschscholzia californica

Eschscholzia californica

June

Dendromecon harfordii

Dendromecon harfordii

July

Romneya coulteri

Romneya coulteri

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Eupatorium purpureum

Eupatorium purpureum

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Epilobium canum sp.

Epilobium canum sp.

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Grevillea spp.

Grevillea spp.

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Drimys winteri

Drimys winteri

December

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