Recently, our family added a Brittany spaniel puppy. Her name is Pompy after the Ompompanoosuc River near our home, and true to the name, she’s a flood risk. 5 a.m. piddle emergencies have us both out on the lawn, welcoming the dawn chorus. Music appreciation is followed by a “what is that you’re chewing?” botany pop quiz. I recommend the Native Plant Trust’s website as a helpful resource for answering such intriguing morning questions as, “is this going to show up as regurgitant on my carpet?” and “should I call the vet?”
It’s true – dogs make you notice nature. Time spent scrutinizing mangled leaf-victims has made me aware that with some exceptions (looking at you, Dutchman’s breeches), most of the toxic plants at my yard’s edge have smooth leaf edges. It’s also prompted me to wonder: why are some leaves toothed, some not?
A skim of scientific papers on the topic suggests that there isn’t one answer. This makes sense; any plant species will have bumped into all kinds of evolutionary pressures along the way. However, broadly speaking, there’s an interplay between leaf edge and climate. For a helpful primer on the topic, check out Weslyan Professor Dana Royer’s research page here, including his note that there’s a correlation between higher annual mean temperatures and the proportion of smooth-edged plant species. As Royer observes, “teeth boost transpiration and photosynthate production early in the growing season, maximizing carbon gain when temperature is limiting.”
Or put another way: we’re toothy up here in the cool woods, proportionately speaking. That’s true of our leaves, and it’s certainly true of our Brittany spaniels. Here’s a photo of Pompy (rhymes with “chompy”) collecting leaf physiognomy data.