48. Mentha L., Sp. Pl. 576. 1753. L., Gen. Pl. ed. 5: 250. 1754; Benth. in DC., Prodr. 12: 166. 1848; Hook. f., Fl. Brit. Ind. 4: 647. 1885; Briquet, Fragment. Monogr. Bot., in Bull. Soc. Bot. Geneve 5: 20-107. 1889; Briquet in Engler & Prantl, Nat. Pflanzenfam. ed. 1, 4, 3A: 3171 1896; Mukerjee in Rec. Dot. Surv. Ind. 14, 1: 85. 1940; Borissova, Labiatae Novae, in Not. Syst. Leningrad 16: 280-285. 1954; Borissova in Komarov, Fl. URSS 21: 597. 1954; Wealth of India, Raw Materials 6: 337. 1962; Hedge & Lamond in Notes Roy. Bot. Gard. Edinb. 28: 94. 1968; Tschernova in Grubov et al., Pl. As. Central 5: 91. 1970; Tucker et al., The Linnaean types of Mentha, in Taxon 29: 233. 1980; Harley in Davis, Fl. Turkey 7: 384. 1982; Press in Hara et al., Enum. Fl. Pl. Nepal 3: 157. 1982; Rech. f., Fl. Iran. 150: 155. 1982; Tuljaganova in Vvedensky, Conspect. Fl. As. Med. 9: 171. 1987.
Perennial variously aromatic herbs of damp or wet places. Stems erect or ascending from a creeping rhizome, glabrous or with simple hairs (in ours), leafy, branched or not. Leaves undivided, serrate or dentate, usually with younger leaves in axils, shortly petiolate or sessile, villous to glabrous, ± gland-dotted abaxially. Flowers borne in many-flowered verticillasters either in axils of upper leaves or in continuous or interrupted spikes of verticillasters subtended by bracts; flowers frequently unisexual and gynodioecious, sometimes gynomonoecious. Calyx small, slightly bilabiate or regular with 5 subequal teeth, tubular-campanulate, 10-13-veined; tube glabrous or villous at throat. Corolla weakly bilabiate, small, with 4 subequal lobes, uppermost slightly larger; tube included within calyx. Stamens 4, subequal and, when fertile, clearly exserted beyond corolla lobes; thecae bilocular, parallel. Style subequally bifid. Nutlets small, ovoid or globose, not trigonous, rounded, smooth or clearly reticulate, mucilaginous on wetting or not.
About 25-30 species in the mainly temperate areas of Eurasia; also in Australia and southern Africa; introduced elsewhere. A distinct genus, but with some major, possibly insuperable, taxonomic difficulties at species level. These difficulties arise from: a very long history of cultivation and naturalization; vegetative plasticity; widespread hybridization; and many different ploidy levels. Sex-forms, usually of male-sterile flowers, are very common; up to c. 40% or more of specimens. Hyper-activity by zealous mint-taxonomists, especially in Europe, led in the past to the creation of a bewildering multitude of taxa of varied rank, but today the approach is more conservative and practical.
The following account of our species is inevitably provisional; many specimens can only be named tentatively. Only specimens seen have been cited, and in the cases of Mentha longifolia and Mentha royleana, by far the most frequent of our species, only a selection of specimens is listed. Literature records have not been included.