Plectranthus amboinicus

Plectranthus amboinicus
Scientific classification
Kingdom:Plantae
Clade:Angiosperms
Clade:Eudicots
Clade:Asterids
Order:Lamiales
Family:Lamiaceae
Genus:Plectranthus
Species: P. amboinicus
Binomial name
Plectranthus amboinicus
(Lour.) Spreng. Syst. veg. 2:690. 1825
Synonyms

Coleus amboinicus Lour.
Coleus aromaticus Benth.

Plectranthus amboinicus, once identified as Coleus amboinicus, is a semi-succulent perennial plant in the family Lamiaceae[1] with a pungent oregano-like flavor and odor. It is native to Southern and Eastern Africa. It is widely cultivated and naturalized elsewhere in the tropics where it is used as a traditional medicine, spice, and ornamental plant.[1] In Thailand, where its leaves are sometimes eaten with meat salad, it is called หูเสือ (/huu-seua/, 'tiger's ear') for the distinctive shape of its leaf.

Description

A Lamiaceae mint plant,[1] Plectranthus amboinicus grows up to 1 m (3.3 ft) tall. The stem is fleshy, about 30–90 cm (12–35 in), either with long rigid hairs (hispidly villous) or densely covered with soft, short and erect hairs (tomentose). Old stems are smooth (glabrescent). Leaves are 5–7 cm (2.0–2.8 in) by 4–6 cm (1.6–2.4 in), fleshy, undivided (simple), broad, egg/oval-shaped with a tapering tip (ovate). The margins are coarsely crenate to dentate-crenate except in the base. They are thickly studded with hairs (pubescent), with the lower surface possessing the most numerous glandular hairs, giving a frosted appearance. The petiole is 2–4.5 cm (0.79–1.77 in). Flowers are on a short stem (shortly pedicelled), pale purplish in dense, 10-20 (or more) flowered dense whorls (cymes) at distant intervals in a long slender spike-like raceme. Rachis 10–20 cm (3.9–7.9 in), fleshy and pubescent. The bracts are broadly ovate, 3–4 cm (1.2–1.6 in) long, acute. The calyx is campanulate, 2–4 mm (0.079–0.157 in) long, hirsute and glandular, subequally 5-toothed, upper tooth broadly ovate-oblong, obtuse, abruptly acute, lateral and lower teeth acute. Corolla blue, curved and declinate, 8–12 mm (0.31–0.47 in) long, tube 3–4 mm (0.12–0.16 in) long. Trumpet-like widened; limb 2-lipped, upper lip short, erect, puberulent, lower lip long, concave. Filaments are fused below into a tube around the style. The seeds (nutlets) are smooth, pale-brown, roundish flattened, c. 0.7 by 0.5 mm (0.028 by 0.020 in).[2]

The aroma of the leaves can be described as a pungent combination of the aromas of oregano, thyme, and turpentine.[3] The taste of the leaves is described as being similar to the one of oregano but with a sharp mintlike pepperiness.[4]

Distribution and habitat

It is native to Southern and Eastern Africa, from South Africa (KwaZulu-Natal) and Swaziland to Angola and Mozambique and north to Kenya and Tanzania, where it grows in woodland or coastal bush, on rocky slopes and loamy or sandy flats at low elevations.[5][6][7] From Southern Africa it would have been carried by Arabs and other traders to Arabia, India and Southeast Asia along the Indian Ocean maritime trade routes. The plant was later brought to Europe, and then from Spain to the Americas, whence the name Spanish Thyme.[5][8]

Traditional medicine and research

In traditional medicine, Plectranthus amboinicus is thought to have medicinal properties,[9] but there is no evidence from clinical research to support such claims. In basic research, the effects of the essential oil were studied in rat models of microbial infections and inflammation,[10] and tested with other plant essential oils for possible use as a mosquito repellant.[11]

Culinary uses

The leaves are strongly flavoured and used for stuffings of meat and poultry, beef, lamb and game.[12][7] The herb is used as a substitute for oregano to mask the strong odors and flavors of fish, mutton, and goat.[8]

Other uses

Traditionally, the herb is applied externally as a mosquito and insect repellent, likely due to essential oils in the leaves.[1] Fresh leaves are used to scent laundry and hair.[1] It is also grown as an ornamental plant.[1][13]

Variegated Cuban Oregano (Plectranthus amboinicus 'Variegatus')

Phytochemicals

The main chemical compounds found in the essential oil of Plectranthus amboinicus are carvacrol (28.65%), thymol (21.66%), α-humulene (9.67%), undecanal (8.29%), γ-terpinene (7.76%), p-cymene (6.46%), caryophyllene oxide (5.85%), α-terpineol (3.28%), and β-selinene (2.01%).[14] Another analysis obtained thymol (41.3%), carvacrol (13.25%), 1,8-cineole (5.45%), eugenol (4.40%), caryophyllene (4.20%), terpinolene (3.75%), α-pinene (3.20%), β-pinene (2.50%), methyl eugenol (2.10%), and β-phellandrene (1.90%). The variations can be attributed to the methodology used in the extraction process, seasonal variations, soil type, climate, genetic and geographical variations of the plant.[15]

Cultivation

Plectranthus amboinicus is a fast-growing plant commonly grown in gardens and indoor in pots. Propagation is by stem cuttings, but it can also be grown from seeds. In dry climates the herb grows easily in a well-drained, semi-shaded position. It is frost tender (USDA hardiness zones 10-11)[16] and grows well in subtropical and tropical locations, but will do well in cooler climates if grown in a pot and brought indoors, or moved to a warm, sheltered position in winter. The plant should be watered only sparingly. In Hawaii and other humid tropical locations, the plant is not to be grown in the shade or part shade, where it will become straggly and unattractive, but rather in the full sun.[3]

Common English names

  • Cuban oregano[17]
  • Country borage (India,[18] South Africa,[7] US[19])
  • French thyme (South Africa,[7] US[19])
  • Indian borage (India[18])
  • Indian mint (South Africa,[7] US[19])
  • Mexican mint (US,[19] favored common name[20])
  • Soup mint (South Africa,[7] US[19])
  • Spanish thyme (US[19])
  • Thick leaf thyme or broad leaf thyme[20]

References

  1. 1 2 3 4 5 6 "Plectranthus amboinicus (Indian borage), Datasheet, Invasive Species Compendium". Centre for Agriculture and Biosciences International. 23 November 2017. Retrieved 28 November 2017.
  2. ↑ Flora Malesiana, Vol. 8, by Steenis, C. G. G. J. van (Cornelis Gijsbert Gerrit Jan); Steenis-Kruseman, M. J. van; Indonesia. Departemen Pertanian; Lembaga Ilmu Pengetahuan Indonesia; Kebun Raya Indonesia, Publication date 1950, p. 387. Available on https://archive.org/details/floramalesiana83stee.
  3. 1 2 Culinary herbs, by Ernest Small, National Research Council of Canada NRC Research Press, 1997, p. 488.
  4. ↑ Florida's Best Herbs and Spices: Native and Exotic Plants Grown for Scent and Flavor, by Charles R. Boning, Pineapple Press Inc, 2010 p. 75.
  5. 1 2 Codd, L. E. W. et al. Flora of Southern Africa : the Republic of South Africa, Basutoland, Swaziland and South West Africa. Vol. 28, part 4, 1981, page 148. Available on Biodiversity Heritage Library at https://www.biodiversitylibrary.org/page/51375271.
  6. ↑ Flora Malesiana, Vol. 8, by Steenis, C. G. G. J. van (Cornelis Gijsbert Gerrit Jan); Steenis-Kruseman, M. J. van; Indonesia. Departemen Pertanian; Lembaga Ilmu Pengetahuan Indonesia; Kebun Raya Indonesia, Publication date 1950, p. 387. Available on https://archive.org/details/floramalesiana83stee.
  7. 1 2 3 4 5 6 "Plectranthus amboinicus". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 21 August 2012.
  8. 1 2 Ethnic Culinary Herbs: A Guide to Identification and Cultivation in Hawaii, by George Staples, Michael S. Kristiansen, 1999, p. 88. Available at https://books.google.com/books?id=jbsdYHEJiDIC&lpg=PA88&ots=I7tNtm5A9w&dq=amboinicus%20oregano%20substitute&pg=PA88#v=onepage&q=amboinicus%20oregano%20substitute&f=false.
  9. ↑ Roshan P, Naveen M, Manjul PS, Gulzar A, Anita S, Sudarshan S (2010). "Plectranthus Amboinicus (Lour) Spreng: An Overview". The Pharma Research. 4: 1–15.
  10. ↑ Manjamalat A, Alexander T, Berlin Grace VM (2012). "Bioactive evaluation of the essential oil of Plectranthus amoinicus by GC-MS analysis and its role as a drug for microbial infections and inflammation" (PDF). International Journal of Pharmacy and Pharmaceutical Sciences. 4 (3): 205–211.
  11. ↑ Lalthazuali; Mathew, N (2017). "Mosquito repellent activity of volatile oils from selected aromatic plants". Parasitology Research. 116 (2): 821–825. doi:10.1007/s00436-016-5351-4. PMID 28013374.
  12. ↑ Dy Phon, Pauline, 2000, Plants Used In Cambodia, printed by Imprimerie Olympic, Phnom Penh
  13. ↑ The Herbalist in the Kitchen, by Gary Allen, University of Illinois Press, 2010, p. 198.
  14. ↑ Senthilkumar, A; Venkatesalu, V (2010). "Chemical composition and larvicidal activity of the essential oil of Plectranthus amboinicus (Lour.) Spreng against Anopheles stephensi: A malarial vector mosquito". Parasitology Research. 107 (5): 1275–8. doi:10.1007/s00436-010-1996-6. PMID 20668876.
  15. ↑ Lopes, P. Q; Carneiro, F. B; De Sousa, A. L; Santos, S. G; Oliveira, E. E; Soares, L. A (2017). "Technological Evaluation of Emulsions Containing the Volatile Oil from Leaves of Plectranthus Amboinicus Lour". Pharmacognosy Magazine. 13 (49): 159–167. doi:10.4103/0973-1296.197646 (inactive 2018-09-10). PMC 5307902. PMID 28216901.
  16. ↑ "Plectranthus amboinicus". Fine Gardening. Retrieved 2017-07-18.
  17. ↑ Gary Allen, The Herbalist in the Kitchen, University of Illinois Press, 2010, p. 198.
  18. 1 2 KALIAPPAN, Nirmala Devi, & Periyanayagam Kasi VISWANATHAN, 2008, 'Pharmacognostical studies on the leaves of Plectranthus amboinicus (Lour) Spreng', International Journal of Green Pharmacy, 2(3): 182-4, http://greenpharmacy.info/index.php/ijgp/article/view/28
  19. 1 2 3 4 5 6 Tropicos, http://www.tropicos.org/Name/17602719, accessed 21 August 2012
  20. 1 2 Encyclopedia of Life, http://eol.org/pages/486424/names/common_names, accessed 21 August 2012
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