Poison Oak
Toxicodendron diversilobum

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Poison oak (Toxicodendron diversilobum ) is a noxious plant found along the west coast of the United States and in areas of southwestern British Columbia.  In California it is so prevalent that it is considered the most hazardous plant in the state and working days lost there to poison oak dermatitis have a significant economic impact.

Poison oak is a deciduous plant with a woody stalk which takes one of two forms depending on whether it is growing by itself in the open or is sheltered by trees or structures. In the open, it appears as a bushy shrub which can reach a maximum of 6 feet (2 metres) in height. In sheltered areas, it is more vinelike supporting itself by clinging to nearby trees, fences or structures and growing much taller.

In general, leaves are composed of three leaflets although leaves of five, seven or nine leaflets are possible as well. In all cases, the stem of the central leaflet is longest. Leaves are notched or toothed and dark green with a paler underside. In spring, the plant can also be identified by the small greenish-white flowers it produces and by its whitish fruit in later summer or early fall. Like many deciduous trees, the leaves of the poison oak change colour in the fall, often turning bright red.

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