It has been an absolute rule: “Leaves of three, let them be.” If a plant has more than three leaves (or leaflets) in a group, then it simply can not be poison ivy.

There have have been extremely rare exceptions. In 50 years I have seen just TWO stalks with 5 leaves. But this week I heard from a very sharp-eyed cyclst named Karin Turer that she had spotted an area of 5-leaf poison ivy along the Arlington bike path in Cambridge. As she sounded very knowledgeable, I went to meet there at the spot, and sure enough there was the smoking gun: an area about 20 x 20 feet of poison ivy ground vine, most all of it sporting an extra set of leaves below the “leaves of three” at the tip.

This is interesting and not necessarily good news, because this variaton may spread and the “leaves of three” rule may have to be set aside.

We harvested many samples and sent them to the major research teams at work on the toxicodendron family. If this is a new species it might be called toxicodenron karin, for Karin Turer, who discovered it.

We will soon be created an entire new webpage, with more images and info about this strange variation on poison ivy. If you have photos of this sort of variation, please send them to us. We want to track the spread of this strange new form of poison ivy.