Bigger and Badder

LARGE poison ivy

As spring rolls around, poison ivy is one of the first plants to emerge. Spring leaves are usually red, but many new leaves are red, so that's not enough to go on. See our ALWAYS-NEVER criteria for deciding if a plant is poison ivy.

However, things are changing in the world of poison ivy. Last season we were alerted to what used to be incredibly rare: poison ivy with more than "leaves of three". Turns out a sharp-eyed cyclist has spottted 5-leaf poison ivy in a number of western suburbs of Boston. We took samples and sent them to various researchers for more study. We don't know why this has started happening, be it some odd effect of road salt, herbicides or climate change.

But what we do know is that poison ivy leaves ARE getting larger due to the increase in CO2 in the atmosphere. A study by Duke Univiversity revealed this a few years ago. The study also revealed that the amount of urushiol, the irritant in poison ivy, is increasing along with leaf size.

Nastier poison ivy is hardly the most serious consequence of more CO2 in the atmosphere, but it is worth taking note of.

When I was a boy in the 1950s, first learning about poison ivy through trial and error, the leaves were rarely more than an inch long. Compare to the photo here, taken last summer, where the leaves are almost bigger than my head!