Peppermint

Peppermint (Mentha × piperita) is a hybrid mint, resulting from a cross between watermint and spearmint. Originating in Europe—specifically England—it has since spread and is now cultivated worldwide.

Among the more than 25 species in the genus Mentha, peppermint is the most commonly used. It is one of the oldest herbs employed for both cooking and medicine, and it serves as a recognized source of menthol and menthone. (Note: Chinese peppermint, or bohe, comes from a different species, M. haplocalyx, though both are accepted plant sources of these compounds.)

Botany

The plant was first documented in Hertfordshire, England, by a Dr. Eales, with John Ray publishing the discovery in 1696. Ray initially named it Mentha spicis brevioribus et habitioribus, foliis Mentha fusca, sapore fervido piperis, later calling it Mentha palustris or Peper–Mint in 1704. It entered the London Pharmacopoeia in 1721 as Mentha piperitis sapore. Carl Linnaeus gave it the name Mentha piperita in 1753, treating it as a species, though it is now recognized as a hybrid between Mentha aquatica and Mentha spicata (with M. spicata itself possibly a hybrid of M. longifolia and M. suaveolens).

Peppermint is a herbaceous, rhizomatous perennial, growing 30–90 cm tall. Its stems are smooth and square in cross-section, with wide-spreading, fleshy rhizomes bearing fibrous roots. Leaves are 4–9 cm long and 1.5–4 cm broad, dark green with reddish veins, acute tips, and coarsely toothed edges; leaves and stems are slightly fuzzy. Purple flowers, 6–8 mm long with a four-lobed corolla about 5 mm across, grow in whorls around the stem, forming thick, blunt spikes.

It flowers from mid- to late summer. Chromosome numbers vary, with 2n counts of 66, 72, 84, and 120 recorded. The plant grows quickly once sprouted.

Ecology

Ecologically, peppermint favors moist habitats like stream sides and drainage ditches. As a hybrid, it is usually sterile, producing no seeds and spreading only vegetatively via runners. Outside its native range, former oil-growing areas often host feral populations, and it is considered invasive in Australia, the Galápagos Islands, New Zealand, and the Great Lakes region of the United States (noted since 1843).

Cultivation

For cultivation, peppermint does best in moist, shaded spots, spreading through underground rhizomes.