Peppermint is considered a sterile hybrid. The parents are spearmint and lemon mint. For a sterile plant, peppermint sure acts like it produces seed. For example, it grows throughout Michigan. One parent, lemon mint has been found only in three northern counties, and two of those collections were more than a century ago. Peppermint has flowers at the ends of branches, without leaves with them. This image is of a plant growing among a patch of peppermint and field mint. Field mint has flowers subtended by leaves, like this. This individual also had bunches of flowers at the ends of branches, which field mint does not. In many ways it was intermediate between the other plants, and tasted like peppermint. It seems very much like a hybrid with a sterile parent!