| Mentha japonica | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Lamiales |
| Family: | Lamiaceae |
| Genus: | Mentha |
| Species: | M. japonica |
| Binomial name | |
| Mentha japonica | |
| Synonyms | |
Mentha japonica is a species of plant in the familyLamiaceae,endemic to the islands ofHokkaido andHonshu, Japan. Initially described asMicromeria japonica byFriedrich Anton Wilhelm Miquel, it was first identified under its present name by JapanesebotanistTomitaro Makino in 1906.[3] A relatively rare plant, it is classified by the JapaneseMinistry of Environment as a Near Threatened species.
Mentha japonica'sbotanical name is derived from its country of origin, Japan. One of itsJapanese-language vernacular name is said to derive from the plant's small size compared to other mint species.[4] In the Japanese literary system ofhanakotoba,M. japonica is used as a metaphor for virtue.[4]
Mentha japonica is now generally accepted as a distinct species by taxonomic authorities,[5][6] but (as with mints generally) the exact phylogenetic tree ofMentha japonica has been difficult to determine due to the genus' tendency to hybridize readily. The species was not included among some 19th or 20th-century academic classifications of the genusMentha.[7] Where it was included, authors have differed on which members ofMentha it is most similar to, and therefore whichsection ofMentha to classify it within. For example, a 1971 paper placed it withMentha arvensis within thesubgenusMenthastrum sect.Verticillatae, on the basis of the presence of flower spikes in the axils of leaves.[8] Conversely, a 2002 author placed it within the sectionEriodontes, along withMentha australis,Mentha diemenica,Mentha satureioides andMentha cunninghamii.[9] However a more recent 2006 survey placed it within the sectionMentha, along with seven other species includingMentha spicata &Mentha canadensis.[10] A 2018 phylogenetic study disputed the placement withMentha, finding it was not closely related to the other mints within the section. These same researchers found a close genetic similarity toMentha gattefossei, because of which they re-proposed the classification ofM. japonica within sectionEridontes.[11] It has also been placed with sectionCapitatae, along withMentha aquatica andMentha dahurica.[12]
Mentha japonica may be categorized as among the mints withmenthol as a primary monoterpene compound (as opposed tocarvone orlinalool), a characteristic it shares with the majority of the genus.[13]
Genetically, along withM. gattefossei andMentha pulegium, it has a basechromosome number of x = 10.[14] It is generally reported to have a somatic chromosome count of 2n = 48.[8][15] It is thought to be either tetraploid or pentaploid.[16]
Viable laboratoryhybridization has been documented betweenM. japonica and theMentha speciesM. canadensis,M. aquatica,M. rotundifolia,M. spicata &M. arvensis.[17][15] A possibility of hybridization withM. dahurica has also been predicted based upon phylogram similarity.[17]
Mentha japonica is a perennial plant which grows to a height of 20-40 centimeters. It spreads and reproduces clonally via thin rhizomes. Its leaves are oblong with entire margins, and its flowers vary from white to pale violet.[18][19] It has an odor similar to pennyroyal (m. pulegium).[20]
The essential oil components ofM. japonica appear to be variable. One 1970 survey found the primary constituents to bementhone (50.8%),isomenthone (18.6%) andpulegone (12.6%). Other chemical constituents identified in smaller amounts include3-Octanone,3-Octonal,d-Limonene,alpha-Pinene,beta-Pinene,Menthyl acetate andPiperitone.[21] These numbers were broadly confirmed by a follow-up survey, but an analysis shortly after (1978) found a significantly higher pulegone content (50%) and lower menthone content (27.9%).[22] A study of wild plants in Hokkaido recorded pulegone content as high as 64.3 to 68%, while experimentally-grown plants inFukushima Prefecture yielded only between 24.8 and 33.9% depending on soil conditions.[23][24]
At least one named variation exists, a long stem variety, form.prostrataSugimoto.[24] This variant grows its stem more than one meter and tends to fall to the ground.[25]
Mentha japonica is endemic to the islands of Hokkaido and Honshu within its native range.[26] It occupies lowland & mountain wetlands, and blooms from August to October in Japan.[19][27]
It is considered a rare plant in its native distribution.[2] According to the Threatened Wildlife of Japan Red Data Book, published by Japan's Ministry of Environment,Mentha japonica is classified as Near Threatened.[1] This is an upgrade from its 2004 classification, which had listed it as Vulnerable.[28] Documented there in the 1940s and 1950s, it is now considered extinct withinAichi Prefecture, due to loss of its preferred habitat.[25]
Like other mints,Mentha japonica is used as both an aromatic herb and as a traditional remedy.[4] Topical ointments containingM. japonica have also been used to treatmastitis in cows.[29]
Data related toMentha japonica at Wikispecies