The first plant I ever learned to definitively identify was poison oak. Growing up in the San Francisco Bay Area, going to science camp in the Santa Cruz mountains, that was the one plant hazard to watch out for. Consequently, it was one of the first we were taught to identify. Later on, when I became an outdoor ed instructor, I always made sure my students knew it if we were in a poison oak zone.

Poison oak is the west coast’s version of poison ivy. It has the same rash-causing oil, urushiol, and the same basic characteristics (“leaves of three, leave it be”), only unlike poison ivy, its leaves are not ivy-shaped. It grows from sea level up to elevations of about 2,500 feet, but no higher. It grows west of the line drawn north to south by the Cascades, the Sierra Nevada, and the Mojave desert, but not east of it. 

Poison oak is a uniquely American plant. While it also grows in a small patch of Mexico (only in northernmost Baja California) and, much more rarely, in Canada (only on the eastern side of Vancouver Island, from what I’ve read), the borders of its range adhere fairly closely to the U.S. states of California, Oregon, and Washington. And it is unique to these states. The rest of the country may have poison ivy and/or poison sumac, but they do not have poison oak. California and the Pacific Northwest states (excluding Alaska, which is too far north) have poison oak, but no poison ivy (and no poison oak either above 2,500 feet). Fun fact: Nevada is the only state in the lower 48 where none of those plants grow at all.

Its three key characteristics are etched in my memory from repeat recitations: smooth stem. Shiny leaves. Leaves in groups of three. But poison oak gets tricky: in the wintertime, from about mid November to mid March, it loses its leaves and becomes just a mass of twigs, unrecognizable if you were counting on its leaves to ID it, but still poisonous. (South of about Santa Barbara, poison oak does not lose its leaves, and its leafless season may have different dates much north of the Bay Area.)

Poison oak is not human medicine. In herbalism school, we learned not to gather medicinal plants that grow near poison oak, because they might be tainted with urushiol. However, it is medicine for the land.

Poison oak, and its fraternal twin wild blackberry (looks like poison oak except that its stem is thorny and its leaves not so shiny, and they often grow together), are what ecologists call primary successors. They like disturbed areas and are among the first to grow where plants have been removed by fire, trampling, or deliberate acts of humans. Poison oak in particular discourages human incursion on land that is healing from disturbance. It is nature’s keep out sign.

If the land is allowed to recover, other plants will move in--secondary succession--and poison oak will start to fade away. With complete recovery of the land, it will eventually disappear completely. 

I have heard of, though never seen, poison oak flower essence (and applaud the brave soul who would make it!). Like other toxic plants, poison oak can safely be used as a flower essence, because flower essences do not contain any of the physical plant. The danger would be in making the essence, which is virtually impossible to do without touching any of the plant. From what I have heard, poison oak flower essence is an especially strong boundary protector. Whereas yarrow, the gentler boundary protector, provides boundaries with an eye to maintaining relationships with others, poison oak screams, “Keep away from me!” It would be used by someone who has such extreme difficulty with setting boundaries that they cannot even begin to imagine boundaries. Perhaps by a survivor of extreme trauma.

This matches poison oak’s role in nature as the keep out sign. If the land has been traumatized, poison oak provides it with space to heal. 

Physical contact with poison oak, however, is not advised. It’s an allergen that everyone is allergic to. While some lucky individuals only react mildly, with just a small rash no more bothersome than a few mosquito bites, others suffer through prolonged severe rashes. In extreme cases, repeated exposure to poison oak could cause anaphylactic shock, the same kind of fatal reaction that kills people who react severely to peanuts or bee stings.

Medicine of plants is not always medicine for us. First and foremost, it must support the land.