Plectranthus amboinicus (Indian borage)

Identity

Preferred Scientific Name

• Plectranthus amboinicus (Lour.) Spreng.

Preferred Common Name

• Indian borage

Other Scientific Names

• Coleus amboinicus Lour.
• Coleus aromaticus (Roxb.) Benth.
• Plectranthus aromaticus Roxb.

International Common Names

• English: country borage; Cuban oregano; French thyme; Indian mint; Mexican mint; soup mint; Spanish thyme
• Spanish: orégano
• French: oreille; ti baume

Local Common Names

• Cuba: orégano; orégano de Cartagena
• Dominican Republic: orégano de Espana; orégano poleo; oreille
• Fiji: rhaivoki; sage
• Germany: Jamaika thymian
• India: pashanabhedi; pathorchur
• Indonesia: daun kutjing
• Lesser Antilles: ditengo; gros thym; soup thyme; thyme; wild thyme
• Malaysia: bangun bangun
• Niue: pasiole
• Philippines: suganda; toronjil de limón
• Puerto Rico: orégano brujo; orégano de Espana
• Samoa: militini
• Sweden: kryddkarlbergare
• Tonga: kaloni; pasiole
• Vietnam: can day lá

Summary of Invasiveness

P. amboinicus is an aromatic herb listed in the Global Compendium of Weeds (Randall, 2012) as “cultivation escape, environmental weed, naturalised, weed” and is known to be invasive outside of its native range including Cuba (Oviedo Prieto et al., 2012) and the Pacific Islands (PIER, 2014). The species reproduces both by seeds and vegetatively (Wagner and Lorence, 2014) and forms dense carpets in shaded dry forest (PIER, 2014). It is considered a common weed in South Africa (Roux, 2003). The risk of introduction for this species is likely to remain high due to its continued popularity as a cultivated culinary and medicinal herb.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Lamiales
•                         Family: Lamiaceae
•                             Genus: Plectranthus
•                                 Species: Plectranthus amboinicus

Notes on Taxonomy and Nomenclature

The Lamiacae, or mint family, is a family of herbs, shrubs, and trees comprising about 200 genera and 3200 species, many with a long history of medicinal and food use (University of Hawaii, 2014). This family includes some of the most well-known herbs containing essential oils including lavender, sage, basil, mint and oregano. Many Lamiaceae species have square stems (although square stems are also found in other families), aromatic aerial parts when crushed, simple opposite leaves, and two-lipped flowers.

Plectranthus is a paleotropical genus comprising around 300 species of annual or perennial herbs or subshrubs, often succulent (Wagner and Lorence, 2014). Its name derives from the Greek words ‘plectron’, meaning ‘spur’, and ‘anthos’, meaning ‘flower’, in reference to the spur-shaped flowers of some members of the genus (Stearn, 1992). Because of the lack of clear-cut morphological criteria to discriminate not only among species within the Plectranthus genus but also among the closely related genera, numerous taxonomic problems in the naming of species have resulted in misplacement of species in several closely related genera like Coleus, Solenostemon and Englerastrum (Lukhoba et al., 2006).

The species P. amboinicus was originally classified under the genus Coleus by Loureiro in 1790 but was moved to the Plectranthus genus by Sprengel in 1825, although both names are sometimes seen in the literature today. P. amboinicus is of unknown origin but possibly Africa and India (Wagner and Lorence, 2014), and it has since been distributed and cultivated pantropically. The type specimen of the species was collected in Amboina, Moluccas, resulting in its species name amboinicus (Roux, 2003). 

Description

Sprawling and somewhat succulent aromatic herb to 1 m high, sometimes subligneous and prostrate at base, the branchlets ascending, densely spreading-hirsute. Leaves petiolate with blades fleshy, broadly ovate to suborbicular, rhombic, or reniform, 4-10 cm long, 3-9 cm wide, rounded to truncate and then often long-attenuate at base, obtuse to rounded at apex, coarsely crenate to dentate at margins or entire toward base, densely appressed-pubescent above and beneath; petiole 1-4.5 cm long. Flowers terminal, spicate, 10-20 cm long, densely pubescent, the verticils 10-20(or more)-flowered, subglobose, the bracts 3-4 mm long, hirsute and glandular; pedicels slender, hirsute, to 5 mm long; calyx campanulate, 1.5-4 mm long, hirsute and glandular, the upper lip erect, broadly ovate-oblong, the other teeth narrow, acute; corolla pale blue or mauve to pink, 8-12 mm long, the tube declinate, 3-4 mm long, expanding distally, pubescent without, the upper lip to 4.5 mm long, 3 mm wide, erect, puberulent, the lower lop to 5-6 mm long, 4 mm wide, concave; stamens with filaments mostly fused into a tube around the style. Fruit nutlets smooth, pale brown, ca. 0.7 mm long, 0.5 mm wide. [Wagner and Lorence, 2014]

In the USA, the species occurs as a perennial shrub (USDA-NRCS, 2014).

Plant Type

Distribution

The origin of P. amboinicus is unknown, but it may be native to Africa and possibly India (Wagner and Lorence, 2014). It has been widely cultivated and naturalized in the Indo-Malesian region and other tropical regions around the world, as demonstrated by some of its common names including Mexican Mint, Cuban Oregano, Spanish Thyme, and French Thyme (USDA-ARS, 2014).

According to Roux (2003), it occurs naturally in Africa from Kenya southwards to Angola in the west and, in the east, to Mozambique, Swaziland and northern Natal.

Although it is known to be cultivated in South America, the species was not included in Funk et al.’s (2007) work on the Guiana Shield or the Brazilian flora of Forzza et al. (2010).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

The origin of P. amboinicus is thought to be tropical Africa, from whence it was introduced into India and then various parts of Asia by early explorers (Hanelt et al., 2001; Roux, 2003; Wyk, 2005; USDA-ARS, 2014; Wagner and Lorence, 2014).). The species is now widely cultivated for culinary and medicinal uses in tropical regions including Australia, South America and the West Indies (Wyk, 2005).

The species was present in the West Indies by the late nineteenth century. It was growing in the Virgin Islands by 1881, Puerto Rico by 1886, Guadeloupe by 1892, Jamaica by 1897, and Cuba by 1912 (Smithsonian Herbarium collections).

Risk of Introduction

Risk of introduction for P. amboinicus is high, as the species is listed in the Global Compendium of Weeds as weedy and an environmental weed (Randall, 2012), and is known to be invasive outside of its native range including Cuba (Oviedo Prieto et al., 2012) and the Pacific Islands (PIER, 2014). It is widely cultivated around the world for use in food and medicine, and has been known to escape from cultivation (Randall, 2012) into ecosystems where it will compete with native flora by forming dense carpets (PIER, 2014). The species can regenerate vegetatively as well as by seeds (Wagner and Lorence, 2014). It is shade tolerant (PIER, 2014). It is considered a common weed in South Africa (Roux, 2003). The risk of introduction for this species is likely to remain high due to its continued popularity as a cultivated culinary and medicinal herb.

Habitat

P. amboinicus is cultivated in gardens and commercial agricultural settings. In Africa it is found at low altitudes in woodland or coastal bush, on rocky slopes and loamy or sandy flats (Roux, 2003). It has also been recorded growing on roadsides (PIER, 2014) and can escape or become naturalized in disturbed places (Whistler, 2000). In Bolivia the species is cultivated in semideciduous forest (Bolivia Checklist, 2014). 

Habitat List

Biology and Ecology

P. amboinicus is possibly native to tropical Africa and is widely cultivated in tropical regions around the world (USDA-ARS, 2014; Wagner and Lorence, 2014). It is known to grow in rocky, loamy or sandy soil (Roux, 2003). The species is tolerant of some shade (PIER, 2014), preferring fertile, well-drained soils in partially shaded areas (Whistler, 2000). P. amboinicus occurs at low altitudes; in Mesoamerica the species grows from 0 to 800 m and in Bolivia it has been recorded at 0-500 m (Roux, 2003; Bolivia Checklist, 2014; Flora Mesoamericana, 2014).

Climate

Soil Tolerances

Soil drainage

• free

Soil texture

• heavy
• light

Means of Movement and Dispersal

P. amboinicus has spread to most tropical parts of the world through intentional human introduction for cultivation. Accidental introduction to the wild has also occurred; the species can regenerate by both seeds and vegetative fragments, and is known to be a cultivation escape (PIER, 2014). Plectranthus species are also used for dry season fodder (Lukhoba et al., 2006), which might also result in further spread.

Pathway Causes

Pathway Vectors

Impact Summary

Environmental Impact

P. amboinicus is known to be invasive in the Virgin Islands, Cuba, and various parts of the Pacific (see Distribution Table), and has a negative impact on ecosystems it has invaded. It competes with native flora by forming dense thickets (PIER, 2014) and can regenerate both vegetatively and by seed (Whistler, 2000; Wagner and Lorence, 2014). It can tolerate a range of soil conditions, shade, and moisture (Whistler, 2000). 

Risk and Impact Factors

Impact mechanisms

• Competition
• Competition - monopolizing resources

Impact outcomes

• Monoculture formation
• Soil accretion

Invasiveness

• Abundant in its native range
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Highly adaptable to different environments
• Long lived
• Proved invasive outside its native range
• Reproduces asexually
• Tolerant of shade
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc

Likelihood of entry/control

• Highly likely to be transported internationally deliberately

Uses

P. amboinicus is widely cultivated as a medicinal plant, potherb, ornamental, and condiment in tropical regions around the world. The aromatic leaves are used as a food additive or spice, flavouring meat, soups, fish, and local beer (Hanelt et al., 2001; Wyk, 2005). The leaves are also eaten as a vegetable, as well as for washing clothes, hair, and laundry due to its fragrance (Whistler, 2000; Wyk, 2005; Lukhoba et al., 2006). The herb is used as a folk remedy for burns and bites, internally as a carminative and antiasthma, and applied externally as an insect repellant, and is also often grown as an ornamental plant for its attractive leaves and flowers (Whistler, 2000; Hanelt et al., 2001). Plectranthus species are also used for dry season fodder (Lukhoba et al., 2006).

In Brazil, the species is often grown in subsistence agriculture (Wyk, 2005). It is used medicinally in Brazil for the treatment of skin ulcerations caused by Leishmania braziliensis, in Malaysia to treat burns and as a poultice for centipedes and scorpion bites, and in India, the juice of the leaves is used to treat skin allergies (Lukhoba et al., 2006). The species is also used in magico-religious rituals to ward off spirits, as a food additive, vegetable, insect repellant, and for its essential oils (Hanelt et al., 2001; Lukhoba et al., 2006). P. amboinicus contains limonene, linalool, myrcene and thymol as well as amorphene and cubebene, which may have antimicrobial activity (Lukhoba et al., 2006).

Uses List

Animal feed, fodder, forage

• Fodder/animal feed

General

• Ritual uses

Human food and beverage

• Spices and culinary herbs
• Vegetable

Materials

• Essential oils
• Pesticide

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Ornamental

• Potted plant

Similarities to Other Species/Conditions

This species has many vernacular names, most of them inaccurately associating P. amboinicus as a mint, thyme, or oregano. P. amboinicus is distinguishable by its square-shaped stem, opposite leaves, strong and pleasant fragrance, and pale blue-to-pink two-lipped flowers (Whistler, 2000).

Gaps in Knowledge/Research Needs

Further research is recommended on control of the species. Since it is a popular and widely used herb, it may continue to escape cultivation and invade native ecosystems.

References

Acevedo-Rodríguez P, Strong MT, 2012. Catalogue of the Seed Plants of the West Indies. Smithsonian Contributions to Botany, 98:1192 pp. Washington DC, USA: Smithsonian Institution. http://botany.si.edu/Antilles/WestIndies/catalog.htm

Bolivia Checklist, 2014. Catalogue of the Vascular Plants of Bolivia, Tropicos website. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria. http://tropicos.org/NameSearch.aspx?projectid=13

Broome R, Sabir K, Carrington S, 2007. Plants of the Eastern Caribbean. Online database. Barbados: University of the West Indies. http://ecflora.cavehill.uwi.edu/index.html

Flora Mesoamericana, 2014. Flora Mesoamericana. St. Louis, Missouri, USA: Missouri Botanical Garden. http://www.tropicos.org/Project/FM

Forzza R, 2010. List of species of the Flora of Brazil (Lista de espécies Flora do Brasil). http://floradobrasil.jbrj.gov.br/2012/

Funk V, Hollowell T, Berry P, Kelloff C, Alexander SN, 2007. Checklist of the plants of the Guiana Shield (Venezuela: Amazonas, Bolivar, Delta Amacuro; Guyana, Surinam, French Guiana). Contributions from the United States National Herbarium, 584 pp.

Govaerts R, 2014. World Checklist of Lamiaceae. Richmond, London, UK: Royal Botanic Gardens, Kew. http://apps.kew.org/wcsp/

Hanelt P, Buttner R, Mansfeld R, 2001. Mansfeld's Encyclopedia of Agricultural and Horticultural Crops (except Ornamentals). Berlin, Germany: Springer.

Humbert H, 1951. Flora de Madagascar et des Comores. Family 175- Labiatae (Flora of Madagascar and the Comoros. Family 175- Labiatae). Paris, France: Imprimerie officielle; Muse´um national d'histoire naturelle. http://www.nhbs.com/title/79635/flore-de-madagascar-et-des-comores-fam-175

Lukhoba CW, Simmonds MSJ, Paton AJ, 2006. Plectranthus: a review of ethnobotanical uses. Journal of Ethnopharmacology, 103(1):1-24.

Merrill ED, 1923. An enumeration of Philippine flowering plants [reprint]. Manila, Philippines: Bureau of Printing. http://www.forgottenbooks.org/books/Botanical_Publications_of_E_D_Merrill_1000888541

Meyer JY, 2000. Preliminary review of the invasive plants in the Pacific islands (SPREP Member Countries). In: Sherley G, tech. ed. Invasive species in the Pacific: a technical review and draft regional strategy. South Pacific Regional Environment Programme, Samoa.

Missouri Botanical Garden, 2014. Tropicos database. St. Louis, Missouri, USA: Missouri Botanical Garden. http://www.tropicos.org/

Oviedo Prieto R, Herrera Oliver P, Caluff MG, et al., 2012. National list of invasive and potentially invasive plants in the Republic of Cuba - 2011. (Lista nacional de especies de plantas invasoras y potencialmente invasoras en la República de Cuba - 2011). Bissea: Boletín sobre Conservación de Plantas del Jardín Botánico Nacional de Cuba, 6(Special Issue 1):22-96.

PIER, 2014. Pacific Islands Ecosystems at Risk. Honolulu, USA: HEAR, University of Hawaii. http://www.hear.org/pier/index.html

Randall RP, 2012. A Global Compendium of Weeds. Perth, Australia: Department of Agriculture and Food Western Australia, 1124 pp. http://www.cabi.org/isc/FullTextPDF/2013/20133109119.pdf

Roux JP, 2003. Flora of South Africa. Cape Town, South Africa: South African National Biodiversity Institute, Compton Herbarium.

Stearn WT, 1992. Stearns dictionary of plant names for gardeners: A handbok on the origin and meaning of the botanical names of some cultivated plants. London, UK: Cassell.

University of Hawaii, 2014. Department of Botany Vascular Plant Family Access Page: Lamiaceae (Labiatae). Honolulu, USA: University of Hawaii. http://www.botany.hawaii.edu/faculty/carr/lami.htm

Urban I, 1898-1928. Symbolae Antillanae: Seu fundamenta florae Indiae Occidentalis. Berolini, Germany: Fratres Borntraeger.

USDA-ARS, 2014. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx

USDA-NRCS, 2014. The PLANTS Database. Baton Rouge, USA: National Plant Data Center. http://plants.usda.gov/

Wagner WL, Lorence DH, 2014. Flora of the Marquesas Islands website. Washington DC, USA: Smithsonian Institution. http://botany.si.edu/pacificislandbiodiversity/marquesasflora/index.htm

Whistler WA, 2000. Tropical ornamentals. Portland, Oregon, USA: Timber Press.

Wyk BEvan, 2005. Food plants of the world: An illustrated guide. Portland, OR, USA: Timber Press, 480 pp.

Links to Websites

Contributors

23/08/2014 Original text by:

Marianne Jennifer Datiles, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA

Distribution Maps

• = Present, no further details
• = Evidence of pathogen
• = Widespread
• = Last reported
• = Localised
• = Presence unconfirmed
• = Confined and subject to quarantine
• = See regional map for distribution within the country
• = Occasional or few reports

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