The black spot test for recognizing poison ivy and related species

A black, enamel-like deposit is frequently present on injured areas of poison ivy, poison oak, and poison sumac. This finding can also be produced deliberately as a field test for the toxic nature of the plant. Observing proper precautions, one crushes sap from leaves onto a sheet of white paper. The resulting stain should darken on exposure to the air if it came from a Toxicodendron. This test employs only one quality of these plants, and it is not, therefore, a substitute for other proved means of identification.