Tag Archives: Torr. and A. Gray

Plant of the day: poison oak

How about an easy one for a Monday! Common and important, unless you want to itch. Poison oak is easy/hard to identify, depending on how experienced you are in looking at plants. The leaves can range in color from dark green to light green to reddish, but they always have a glossy shine and another quality as well, one that’s distinct but hard to define. The leaves look… slightly luminous. Tender. As if, were you crazy enough to nibble on one, it would have a pleasant delicate texture.

The flowers of poison oak are small, inconspicuous, and not usually in bloom, so the leaves are what to look out for. These always come in groups of three, and they have a smooth surface, the veins only showing lightly and the surface not haired or spined. The edges are gently lobed or scalloped – to varying degrees, but they are neither straight nor serrated (like the edge of a bread knife). This helps you rule out other common plants, like blackberry, that some people confuse for poison oak. Once you get all those features down, really the only thing that looks similar are the leaves of a young true oak tree before it has grown tall.

The Latin name is easy to remember as well (even though I had forgotten it). Toxicodendron diversilobum. Intuitive, right? Toxic leaf with diverse lobes. Thanks John Torrey, Asa Gray, and Edward Greene who did the naming. Torrey produced the Flora of North America in the 1800s, and Gray helped him out. And how do I know they named our toxic friend, a newbie may ask? It says so right on all the official listings of the species. Check the names after the italicized species name on the above link: you’ll see Torr. and A. Gray, who did the original naming, along with Greene, who came along later and made some change – I’m not sure but maybe he is responsible for the “Toxicodendron”, since I seem to remember poison oak was a “Rhus” when I first learned it. Anyway this convention is called an author citation, with the namers being the “taxon authors“.

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Filed under Botany basics, Native, Plant of the day, Poisonous