Erin came back from a neighborhood foraging expedition today bearing a sprig of this "mint" in her sure hand. It doesn't exactly look like either spearmint or peppermint, with its slightly rounded leaf edges and more shallowly etched veins. Nevertheless, as my steadfastly adventurous vegetable companion declared:
"Well whatever it is, it tastes like mint. And I haven't died yet."
I can still hear deliberate and industrious noises coming from the kitchen, where Erin is allegedly making tortellini from scratch. Any more specific i.d.'s on this minty plant are welcome.