Peppermint (Mentha × piperita) is a (usually) sterile hybrid mint, a cross between watermint (Mentha aquatica) and spearmint (Mentha spicata). It is occasionally found wild with its parent species in central and southern Europe, but the first intentional crossbreed of watermint and spearmint was done in England. Being sterile, it spreads by rooting.
The stems are from 30-70 cm tall, rarely up to 100 cm, smooth, and square in cross section. The leaves are from 4-9 cm long and 1.5-4 cm broad, dark green with reddish veins, and with an acute apex and coarsely toothed margins. The flowers are purple, 6-8 mm long, with a four-lobed corolla about 5 mm diameter; they are produced in whorls around the stem, forming thick, blunt spikes. Flowering is from July to September.