Mentha piperita L. - Peppermint

Mentha piperita plant

Family - Lamiaceae

Stems - Multiple from the base, from fibrous roots, erect, branching, herbaceous, rotting at the nodes, 4-angled (the angles rounded), glabrous, to +1m tall, fragrant.

Leaves - Opposite, decussate, petiolate. Petioles to 1.5cm long, glabrous to sparse pubescent, minutely winged from decurrent leaf tissue. Blades to 9cm long, -4cm broad, glabrous but with some pubescence on midrib below, rounded at the base to slightly tapering, elliptic lanceolate, serrate, acute, punctate. Veins anastomosing, depressed adaxially, expressed abaxially.

Mentha piperita leavesPressed leaves.

Inflorescence - Terminal spikiform cluster of axillary verticels. Each axillary cluster with +/-20 flowers. Clusters subtended by lobed bracts which often exceed the clusters. Pedicels purple, glandular, to 2mm long.

Flowers - Corolla lilac, glabrous internally and externally, 4-lobed (weakly bilabiate), to -4mm long. Lobes subequal, rounded at the apex, +1mm long. Upper lobe notched at the apex and slightly larger than the 3 lower lobes. Stamens 4, adnate at the apex of the corolla tube, alternating with the corolla lobes, included. Filaments white, .5mm long. Anthers orange, .4mm long. Ovary superior, deeply 4-lobed, glabrous, green, .6mm broad, subtended by a thick green nectary. Style white, glabrous, -5mm long, exserted. Stigma 2-lobed. Calyx tubular, often purplish, glabrous internally, glandular externally, 10-ribbed, 5-lobed, the tube to 2mm long. Lobes to 1mm long, triangular-attenuate, ciliate-margined. The sinuses between the lobes rounded.

Mentha piperita flowers

Flowering - June - October.

Habitat - Wet ground of meadows, spring branches, streams, pond margins, sloughs, ditches, roadsides, railroads.

Origin - Native to Europe.

Other info. - This weedy species is the common "Peppermint" of flavorings. The plant can be found scattered throughout Missouri and is fairly common. It is always associated with wet conditions.
The plant has a variety of culinary uses which need not be mentioned here. Menthol, derived from the plants oil, is used in many pharmaceuticals.
M. piperita and the closely related M. spicata L., (Spearmint) grow well from seed and can be cultivated easily.
M. spicata is very similar but has sessile to very short petiolate leaves.

Photographs taken at the Peck Ranch Wildlife Refuge, Carter County, MO., 7-19-01.