Friday, March 6, 2009

Poison oak - the shapeshifter

Poison oak seems like one of the hardest plants to identify, especially to those who are not botanically-inclined. But it seems like it is the one plant everyone on trails wants to be able to identify so they can avoid its agonizingly itchy effect on the skin.

But why is poison oak so hard to identify? One main reason is that, although it is a perennial vine, it is deciduous - therefore, its leaves turn colors (generally red) in the fall and then drop off in the winter. This also means that, in the winter, it just looks like a bunch of dead branches until you accidentally brush up onto one or, heaven forbid, snap one with your hands! See photo above.

This also means that in the spring, when the new leaves emerge (for many that is right now), they are very small and it is difficult to discern the typical "leaves of 3, let it be" leaf arrangement. The young leaves are also generally a reddish color, as opposed to the deep green of the mature leaves. See photo to the right.

However, even the mature leaves can look different depending on their location. Leaves that are in full sunlight are often smaller and glossy with toxic oils, while leaves in full shade are often big and sometimes lack that glossy shine. See photo to the left - this plant is in partial sun.

So, if all else fails, and you can't remember the phrase "leaves of 3, let it be" then fall back on the phrase "when in doubt, do without" and avoid it!

If you would like to learn more interesting facts about poison oak (for example, that it is related to pistachios!) please read our previous blog from July 2, 2008 in the Archives.

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