Leaves of three, let it be? VT researchers find spotting poison ivy may be more complicated
BLACKSBURG, Va. (WFXR)– When talking about poison ivy, we’ve all heard the classic saying, ‘Leaves of three, let it be.’ While this specific rhyme exists to prevent people from touching poison ivy, there are also many harmless three-leaf native plants. So, how is someone able to tell the difference?
Virginia Tech researchers found that poison ivy leaves show a lot of variabilities that can change accurate poison ivy plant identification and undermine the longstanding avoidance saying.
“Based on the research, poison ivy had enormous amounts of leaf variation,” said John Jelesko, associate professor in the School of Plant and Environmental Sciences. “There was no clear poison ivy look. It was quite astonishing, especially since the data set included poison ivy plants from all over the geographic United States.”
In the research project, funded by the Department of Agriculture Hatch Grant administered by the Virginia Agriculture Experiment Station, VT research used around 2,000 poison ivy photos from iNaturalist.org to compare leaf shape variability across the United States.
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The records for poison ivy and American hog peanut, a three-leafed plant commonly confused with poison ivy, were analyzed for seven attributes related to the shape of their compound leaves. These attributes were used to calculate a total leaf complexity score, finding the average and range for poison ivy significantly higher compared to the American hog peanut.
Further analyses confirmed that the spread of poison ivy’s leaf shape variability was greater as well.
Also, the total leaf complexity showed a high degree of variation across North America. Despite this, researchers found a noticeable trend of increasing total leaf complexity in poison ivy from east to west, with more serrated edges on leaves further west.
Researchers also identified poison ivy plants with five leaves during the study, which came in two different orientations.
“Whatever this [variable leaf shape] phenomenon is, it is widespread and inherent to the plant,” Jelesko said. “Our ultimate recommendation is that avoidance by identification is not going to work well because the basic step of identification is problematic at best.”
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