California Poison Oak

Pacific poison oak, or Toxicodendron diversilobum, is a serious problem plant. Although it grows almost only in California, a lot people encounter it there. It grows as a ground vine, as a shrub, and as a climbing vine.
pacific poison oak broad leaves

Pacific Poison Oak With Broad Leaves.

In California you will see huge differences in the size, shape, and color of poison oak leaves. It depends on how much moisture, how much light, the type of soil, plus natural variations.

pacific poison oak

Fall Pacific Poison Oak Leaves.

These leaves have much more pointed leaves, much like eastern poison ivy.

pacific poison oak leaves

Oak-like Pacific poison oak leaves.

This plant has the typical leaf shape that reminds people of oak leaves. But notice how it doesn’t look like the two examples above.

Pacific poison oak with extra leaf

The Rare But Real 5-leaf.

California poison oak has 5-leaflet leaves often enough that you can spot them (whereas eastern poison ivy has them so rarely that few people have every seen them.)

pacific poison oak narrow leaves

A Long Center Stem

Compared to the examples above the very long center leaf stem is odd, but poison oak has endlessly different looks.

pacific poison oak next to thorny vine

Poison Oak with a Thorny Neighbor

On the left is a shiny poison oak plant, but on the right is a thorny vine: poison oak NEVER has thorns!

pacific poison oak stalk

Poison Oak Stalk

When the plant grows as a shrub it sends up very straight stalks. This is a good place to see the way the leafs come off the stem alternating left then right. 

Pacific poison oak green berries

Poison Oak Berries

Notice how the berries have deep grooves from top to bottom, like tiny pumpkins.

pacific poison oak with berries

Poison Oak Berries

Here are bunches of berries in the fall, hanging down. They are good food for birds; clearly NOT for people.

pacific poison oak climbing tree

Poison Oak Begins to Climb

Until the vine gets its first wrap around the tree it doesn’t have a strong grip.

pacific poison oak climbing tree

Poison Oak Climbing a Tree

Pacific poison oak climbs trees, usually by wrapping around them. (Eastern poison ivy attaches with hairy roots, which seems a much more effective way to climb.)

pacific poison oak swarming a tree

Poison Oak Swarming a Tree

This shows that poison oak will grow wildly up a tree once it gets started. It doesn’t kill the tree, but does compete for water and nutrients.

Pacific poison oak climbing tree

Poison Oak Climbing a Tree

The vine is working its way up the tree and will climb as high as it can.

pacific poison oak climbing tree

Poison Oak Climbing an Evergreen

This this tree is becoming host to a pretty big poison oak vine.

pacific poison oak large shrub

Poison Oak As A Large Shrub

This poison oak shrub is about 15 feet tall, a common sight throughout much of California.

pacific poison oak on dry hillside

Poison Oak Fence Shrub

Poison oak will grow along a fence at the edge of very dry fields, as we see here.

pacific poison oak by Golden Gate bridge

Poison Oak At The Golden Gate

The entire hillside facing the Golden Gate Bridge on the northern side was covered with huge stands of poison oak.

pacific poison oak curly near ocean

Poison Oak Curly And Waxy Near Ocean

Poison oak that grows near salt water will take on a curly and waxy look, just like poison ivy does along the Atlantic Ocean.

roadside pacific poison oak

Poison Oak Along The Road

Driving up to Yosemite there was poison oak growing up to a certain altitude beyond with it doesn’t grow (same with poison ivy in the east.)

extensive hedge of pacific poison oak

Deep Poison Oak Hedge

Poison oak forms a 50-yard dense hedge between a trial and the drier hillside beyond.

California runner near poison oak

Jogger Passing By Poison Oak

This jogger is passing long trailside growths of poison oak. He has to be careful not to brush against the shrubs or he will pay the price.

pacific poison oak growing in shade

Poison Oak Hiding in the Shade

In hot and dry areas California poison oak will sometimes grow in the shadow of other plants that are less sensitive to sun. The poison oak is the darker plant in the bottom third.

pacific poison oak over a trail

Poison Oak Overhead

This trail had a growth of poison oak ABOVE the heads of walkers. Most people would not expect to see poison oak above them. (the plant nearer is a tree; the shrub hanging over in the center of the photos is the poison oak.)

pacific poison oak by park entrance

Poison Oak Welcoming Hedge

At the entrance to this park right behinds all the welcome signs was a huge hedge of poison oak.

pacific poison oak square dance club

Poison Oak Square Dance Club

Poison oak is a big part of California lore; this square dance club named themselves after it.

Pacific poison oak always-never chart

This diagram shows some things to look for: Pacific poison oak rarely has more than 3 leaves in a group. And it never has thorns or saw-tooth edges.