Mentha longifolia

Mentha longifolia, also known as horse mint, brookmint, fillymint or St. John's horsemint, is a species of plant in the family Lamiaceae. It is native to Europe excluding Britain and Ireland, western and central Asia (east to Nepal and far western China), and northern and southern (but not tropical) Africa.

Description
It is a very variable herbaceous perennial plant with a peppermint-scented aroma. Like many mints, it has a creeping rhizome, with erect to creeping stems 40–120 cm tall. The leaves are oblong-elliptical to lanceolate, 5–10 cm long and 1.5–3 cm broad, thinly to densely tomentose, green to greyish-green above and white below. The flowers are 3–5 mm long, lilac, purplish, or white, produced in dense clusters (verticillasters) on tall, branched, tapering spikes; flowering in mid to late summer. It spreads via rhizomes to form clonal colonies.

Taxonomy
Mentha longifolia has been widely confused with tomentose variant plants of the species Mentha spicata; it can be distinguished from these by the hairs being simple and unbranched, in contrast to the branched hairs of M. spicata.

Infraspecies
The following subspecies and varieties are recognised:
 * Mentha longifolia var. amphilema Briq. ex Rech.f. - western Asia
 * Mentha longifolia var. asiatica (Boriss.) Rech.f. - western Asia to western China
 * Mentha longifolia var. austroafghanica Rech.f. - Afghanistan
 * Mentha longifolia subsp. capensis (Thunb.) Briq. - southern Africa
 * Mentha longifolia var. chlorodictya Rech.f. - Caucasus to western & central Asia
 * Mentha longifolia var. kermamensis Rech.f. - Iran
 * Mentha longifolia var. kotschyana (Boiss.) Briq. - eastern Turkey, Iran
 * Mentha longifolia subsp. longifolia (L.) L. - Europe, northwestern Africa
 * Mentha longifolia var. muqarrabica Shinwari & Chaudhri - Pakistan
 * Mentha longifolia subsp. noeana (Briq.) Briq. - Turkey east to Iran
 * Mentha longifolia var. petiolata Boiss. - northern Iraq to northern & western Iran
 * Mentha longifolia var. schimperi (Briq.) Briq. - Sinai to Arabian Peninsula
 * Mentha longifolia var. swatica Shinwari & Chaudhri - Pakistan
 * Mentha longifolia subsp. typhoides (Briq.) Harley. - northeastern Africa, southwestern Asia
 * Mentha longifolia subsp. wissii (Launert) Codd. - southwestern Africa

Hybrids
Mentha longifolia hybridizes with other Mentha species. Hybrids include:
 * Mentha × villosa-nervata Opiz. (hybrid with Mentha spicata) sharp toothed mint
 * Mentha × rotundifolia (L.) Huds., 1782 (hybrid with Mentha suaveolens) false apple mint

Varieties and Cultivars
Unlike other commonly cultivated species and hybrids of mint, there are few horticultural cultivars of M. longifolia. The only ones of note are:
 * M. longifolia Buddleia Mint Group (syn. M. longifolia 'Buddleia') - with silvered leaves.

Cultivation
Like almost all mints, Mentha longifolia can be invasive. Care needs to be taken when planting it in non-controlled areas.

Uses
Nicholas Culpeper's Complete Herbal (1653) states that "It is good for wind and colic in the stomach ... The juice, laid on warm, helps the King's evil or kernels in the throat ... The decoction or distilled water helps a stinking breath, proceeding from corruption of the teeth, and snuffed up the nose, purges the head. It helps the scurf or dandruff of the head used with vinegar." In addition, Mentha longifolia, like other Mentha species, is known to have important medicinal properties.