Papalo (Porophyllum ruderale) is a bold, raw-eaten Mexican summer herb whose rounded, blue-green leaves taste like cilantro turned up loud — a pungent collision of coriander, arugula, rue and citrus with a soapy, almost gasoline edge. Eaten fresh and never cooked, it is the signature herb of the Puebla cemita and a hot-weather stand-in for cilantro, which bolts and fails in the same heat that papalo thrives in.