Plant extracts used to heal disease and disorders date back to ancient times. The earliest apothecaries that relied heavily on plant extracts surfaced among ancient civilizations including the Babylonians in Mesopotamia (4000-5000 BC), and also among the Egyptians, Greeks, Aztecs, and the Inca, who occupied the South American region of the Andes (Van Wyk et al., 1997; Jacome, 2003; Lock et al., 2016).
The geography and climate of the Andean region is unique, ranging notably in altitude, temperature, and in precipitation and solar radiation indexes. Consequently, the region contains a high number of diverse plant varieties with broad functional properties that are desired on both a local and global scale (Brack, 1999). More than 500 Andean medicinal plants alone are utilized on a local scale primarily for the treatment of urinary tract infections, magical/spiritual ailments, respiratory disorders, and pest management; and globally, their essential oils are of commercial and pharmaceutical interest (Banchio et al., 2005; Boulogne et al., 2012; Monigatti et al., 2013).
Of the 500+ Andean medicinal plants, those within the genus Minthostachys, South America’s Andean mint, have been used in traditional medicine as early as the16th century. They are considered to be some of the most important plants of the Andes because of their therapeutic, insecticidal, pesticidal, and aromatic properties, their commercial value as a condiment and flavour enhancer, and their pharmaceutical value as a bactericide, fungicide, and viricide (Schmidt-Lebuhn, 2008).
The genus Minthostachys (synonymous with Bystropogon) is commonly referred to as Muña, and belongs to the Lamiaceae [Mint] family. Distributed along the Andes, from Venezuela to Argentina, it is a perennial subshrub that grows between 1600-3200 m above sea level, measures up to 1.2 m, has small to medium leaves varying from 1-5 cm long to 1-3 cm wide, and seasonal white flowers (De Feo, 1992; Pastoriza, 2013; Alkire et al., 1994).
Originally believed to consist of 12 aromatic species, systematic and taxonomic work within the last decade revealed that Minthostachys is minimally comprised of 17 species (Table 1). Unfortunately, many years of taxonomic complications due to morphological variability within the genus, together with a lack of voucher specimens, resulted in many undetermined or wrongly identified species labelled universally as M. mollis. Consequently, these issues should be considered when reviewing more dated botanical, chemical, and pharmacological research limited to possibly Peruvian M. mollis and Argentinian M. verticillata (Schmidt-Lebuhn, 2008).
Given these pitfalls in the data, reported therapeutic properties may not represent the correct species. And even honest attempts to correctly identify a species may fall short simply because of poorly documented descriptions of the morphological variation among the leaves, stems, and inflorescences – which happen to be the plant parts extracted for essential oil (Schmidt-Lebuhn, 2008).
There are a number of documented ailments treated by essential oils or extracts under the ambiguous umbrella term of Minthostachys, including anxiety, insomnia, colitis, flatulence, stomach ache, diarrhea, the common cold, influenza, dizziness, altitude sickness, bronchitis, asthma, bacterial infections, sepsis, fungal infections, and internal parasites (Ramos, 1979; White, 1985; Economou and Nahrsted, 1991; De Feo et al., 1998; Lock et al., 2016).
Conversely, research has been conducted on the therapeutic properties, chemical profiles, and traditional uses of unambiguous Minthostachys species endemic to Peru, Colombia, Bolivia, Venezuela, Ecuador, and Argentina. The majority of said research has occurred in Peru and Argentina, which may be positively correlated to the fact that the essential oils of Minthostachys species endemic to these countries are extracted on a commercial scale (Schmidt-Lebuhn, 2008). An overview of what is known about various and confirmed Minthostachys species begins in Peru.
Peruvians commonly refer to M. mollis as Muña, Tento, Tinot, Menta, Toronjil, Chancua, Champca, or Ishmuna. Vernacular names among locals may be in accordance to ‘Muña’s’ distribution. For example, subshrubs growing between 2000-3500 m are referred to as muna blanca (white mint) [likely M. mollis var. mandoniana] and muna negra (black mint) [likely M. acris]; a small pungent subshrub that grows above 3500 m is known as muna menuda (small mint) [likely M. mollis, M. acris, or M. setosa] (Figure 1); and a creeping shrub that grows on stony slopes is likely M. spicata (Schmidt-Lebuhn, 2008; N. Zambrano, personal communication October 15, 2015; Solis-Quispe et al., 2016).
Quechua communities in the high Andes implement a hot and cold traditional medicinal system (Figure 2). In a manner comparable to the theory of yin and yang in traditional Chinese medicine, the Quechuan system holds that hot and cold forces are naturally balanced in a body free of disease and disharmony. An imbalance is caused by an excess of one of these forces, thereby resulting in a hot or cold disease. As a general rule, cold plants are used to treat hot diseases, and hot plants are used to treat cold diseases. Plants are therefore categorized according to their hot and cold properties, as well as their distribution.
Muña is classified a “very hot” herb because it grows in the wild at high altitudes fully exposed to the sun, and because its strong aromatic pungency has made it indicated empirically for a wide range of ailments of a cold nature. Examples of cold disorders addressed by Muña include musculoskeletal pain and inflammation caused by repeated exposure to high altitude-glacier water, influenza, the common cold, and respiratory conditions caused by cold winds that have penetrated the body following profuse sweating from intensive physical labour (De la Cruz et al., 2014).
Minthostachys extracts used in traditional medicine are administered orally, topically, and via inhalation (Schmidt-lebuhn, 2008; Monigatti et al., 2013; De la Cruz et al., 2014; Ablard, 2016). Ingestion of M. mollis, M. acris, M. setosa, or M. spicata decoctions, infusions, teas, and essential oils are used for their digestive, carminative, parasiticide, diuretic, sedative, and aphrodisiac properties, and to reduce the symptoms of diarrhea, gastritis, and colitis (Hammond et al., 1998; Schmidt-Lebuhn, 2008; Ablard, 2016; Lin Ylla, personal communication, December 14, 2017) (Table 1).
Topical applications of M. mollis, M. setosa, and M. spicata in the form of warmed leaves, or essential oil rubbed directly onto the body, or poultices are used to treat aire1, susto2, joint inflammation, rheumatism, arthritis, contusions, and bacterial and fungal infections, and to help reduce wrinkles and soften the skin (Schmidt-Lebuhn, 2008; De la Cruz et al., 2014; Victor Huaman, personal communication, April 2, 2017; Lin Ylla personal communication December 14, 2017) (Table 1).
Inhalation of M. mollis, M. setosa, and M. spicata essential oil directly from the bottle or via steam baths helps to regulate menstruation, and to treat symptoms associated with insomnia, anxiety, aire, susto, headaches, nausea, bronchitis, coughs, and asthma. Headaches and respiratory conditions are common ailments for people living in Andean mountain communities because of the cold temperatures and strong winds (Schmidt-Lebuhn, 2008; Monigatti et al., 2013; Ablard, 2016; Victor Huaman, personal communication, April 2, 2017).
Peruvians also use fresh leaves or leaf extracts of M. mollis var. mandoniana, M. spicata, and M. acris to protect their food from putrefaction and pests (Aliaga and Feldheim, 1985; Economou and Nahrsted, 1991; Carvajal and Thilly, 1998; Hammond et al., 1998; De la Cruz et al., 2014), and as a repellent against insects that transfer Chagas disease (Hurtado et al., 1987; Schmidt-Lebuhn, 2008). The essential oil of Minthostachys andina in Bolivia has also been found to be effective against Chagas disease vectors’ Rhodnius neglectus and Triatoma infestans, and to repel pests from crops (Bastien, 1983; Girault, 1984; Fournet et al., 1996). Infusions of M. andina leaves are used in traditional medicine to treat migraines, headaches, heart palpitations, rheumatism, inflammation, anemia, fever, diarrhea, and bacterial infection (Fournet et al., 1996).
Similar to the essential oil of Peruvian M. mollis and Bolivian M. andina, Colombian M. mollis essential oil contains antibacterial properties, specifically against Staphylococcus aureus, S. epidermis, and Escherichia coli, which are thought to be linked to its unique chemical composition inclusive of carvacrol and thymol (Torrenegra-Alarcon et al., 2016) (Table 2). Colombian M. mollis essential oil has also been shown to inhibit the onset of human herpes viruses HHV-1 and HHV-2 infections (Brand et al., 2016).
Venezuelan M. mollis essential oil has shown to be highly effective against the Gram-positive bacterium Bacillus subtilis, and the Gram-negative bacterium Salmonella typhi (Mora et al., 2009). It is used in traditional medicine as an antihistaminic (Malagón et al., 2003).
Ecuadorian M. mollis is commonly referred to as Tipo, Tipillo, Poleo, Pumin, or Muña, and has a distinct peppermint-like odor. Infusions of its leaves are used in traditional medicine as a digestive, antispasmodic, and to help treat head colds, stomach aches, and irregular menstruation; whereas decoctions are used to help combat muscle pain and rheumatism (Acero Coral and Rive 1989; Alkire et al., 1994; Malagón et al., 2003). Its leaves are smoked to help treat headaches and asthma (White, 1985), while the whole plant is rubbed over the body, or a leaf extract is inhaled, to treat mal aire/mal viento3 and espanto4 (Rubel, 1964; Finerman, 1983; 1987). The essential oil, rich in menthol and menthone, has been shown to be effective against influenza (Alkire et al., 1994; Malagón et al., 2003; Cavender and Alban, 2009) (Table 2).
Minthostachys verticillata, often and mistakenly referred to as M. mollis, is the only endemic Minthostachys species to Argentina, and it is commonly known as Peperina and Piperina. Its essential oil, commercially distilled as early as 1913 (Doering, 1913), has been shown to inhibit quorum sensing (QS) which could explain its extremely high antimicrobial activity against certain bacteria (Goleniowski et al., 2006; Pellegrini et al., 2014). Bacteria affected by M. verticillata essential oil are Listeria innocua, Staphylococcus aureus, Bacillus subtilis, B. cereus, Streptococcus faecalis, Proteus mirabilis, E. coli, and S. typhi. The oil also contains antiviral properties against herpes and pseudorabies, and has been shown to possess fungicidal, nematicidal, and antioxidant properties, as well as a capacity to suppress allergic reactions of basophils and lymphocytes (Schmidt-Lebuhn, 2008; Pellegrini et al., 2017). Its branches and leaves are used in traditional medicine to treat diarrhea, impotence, respiratory conditions, and urinary tract infections (Anesini and Perez, 1993; Schmidt-Lebuhn, 2008). Further, it is an effective repellent against the dengue and Zika virus vector, Aedes aegypti (Gillij et al., 2008; Palacios et al., 2009).
Although there is a plethora of research on the therapeutic benefits and indications of Minthostachys’ essential oils, guidelines on its safety were not indicated. Due to the lack of this important information coupled with the steadily growing importation of these oils to North America for their use in integrated medicine, Robert Tisserand provided a safety summary to work from. The summary is based on 43-47% pulegone, 14-19% menthone, and 13-15% isomenthone, chemical constituents predominantly found in Peruvian M. setosa and M. spicata (Table 2). He states that, neither menthone nor isomenthone present any known or likely safety issues, and there are no minor constituents in quantities that raise red flags. Pulegone is potentially hepatotoxic and neurotoxic, and Schmidt-Lebuhn (2008) refers to the presence of up to 47% pulegone in M. verticillata. According to Tisserand and Young (2014) this concentration of pulegone would suggest a topical maximum concentration of 2.5%. The maximum daily oral dose for a 70 kg adult would be 35 mg (approximately one drop). (R. Tisserand, personal communication, December 19th, 2017).
Chemistry and Biological Activity
The predominant and prevalent chemical constituent within the genus Minthostachys is the monoterpene ketone pulegone (Table 2; Figure 3). Two enantiomeric forms naturally occur; the R-(+)-enantiomer is the most abundant in essential oils.
Pulegone has been shown to be the compound linked to repulsion activity against the dengue fever mosquito, Aedes aegypti, and this activity is enhanced when pulegone is coupled with high concentrations of limonene (Gillij et al., 2008). Minthostachys species with these chemical profiles include Venezuelan M. mollis, and Peruvian M. mollis from the Pampas region (Table 2). It’s well documented that plants with insecticidal properties tend to include not only pulegone, but also the terpenoids limonene, linalool, and menthone, which in combination have shown to be effective pesticides against the house fly and German cockroach (Boulogne et al., 2012). Minthostachys species with these chemical profiles are Venezuela M. mollis, Peruvian M. setosa, and M. spicata (Table 2).
The most cited plant family with species possessing insecticidal and fungicidal properties is the Lamiaceae family (Janssen et al., 1987; Boulogne et al., 2012). Antifungal chemical constituents not listed in this report are the terpenoids borneol, citronellol, linalool, thymol, and eugenol. These are all present in Peruvian M. setosa, known for its extremely high efficacy against fungi.
Additional chemical constituents among many Menthostachys species include menthone, isomenthone, germacrene D, and limonene (Table 2). Menthone and isomenthone are well documented for their antioxidant properties and thus free radical scavenging activity (Mimica-Dukic et al., 2003). Minthostachys essential oils that contain both these constituents, and fall within the range of scavenging activity, include M. andina, Ecuadorian M. mollis, Peruvian M. setosa, and M. spicata.
As is the case with most essential oils, chemical compositions are subject to extreme variation contingent on genetic factors that may in turn be influenced by climate, season, distillation method, geographical conditions, and harvest period. For example, the essential oil of M. verticillata leaves and flowers harvested in June differ in therapeutic properties than those harvested in other months (Pellegrini et al., 2017). Venezuelan M. mollis distributed at 1600 m contained higher amounts of α-pinene, β-pinene, limonene, linalool, pulegone, 1,8 cineole, and piperitone, and lower amounts of isomenthone and menthone, than M. mollis distributed at 3600 m (Rojas and Usubillaga, 1995). Also affecting the ratio of pulegone to menthone is elevation and the gradient of an Andean slope in the same location, as documented for the essential oil of M. andina (Munoz-Collazaros et al., 1993). Essential oil extracted from damaged M. verticillata leaves can also affect the concentration of menthone and pulegone increasing it six and four times respectively when compared to essential oil extracted from non-damaged leaves (Banchio et al., 2005). Concentrations of other constituents such as carvacrol and thymol, known for their pronounced antibacterial activity (Torrenegra-Alarcon et al., 2016) may be quite high, but rarely present in Minthostachys species with the exception of Colombian M. mollis (Table 2). And interestingly, the chemical profile of Peruvian M. mollis varies from region to region, with some species containing 1-tetradecene, a constituent virtually absent in other Minthostachys species (Fuertes-Ruitón and Munguia-Chipana, 2001) (Table 2).
Understanding the environmental chemistry of Minthostachys spp. is just one area that must be further explored in order to deepen our understanding and preservation of this genus, which we know so very little about. Building upon and reassessing our current modicum of knowledge through clinical research, systematic taxonomic classification, conservation genetics, population density assessments, and sustainable management of these plants are of equal importance.
Although no Minthostachys species is classified as threatened, it is possible that some species may be. Approximately 80% of the global population relies on plant-based medicine to treat, and support the healing of, numerous health issues (Akhtar et al., 2014; Arumugam et al., 2016). Specifically, essential oil-based products and their chemical compounds are in high demand by the cosmetic, perfume, food flavoring, and pharmaceutical industries; more than 250 unique essential oils are annually traded on the international, valued at ~1.2 billion USD (Akhtar et al., 2014; Swamy and Sinniah, 2016).
This high demand is often the underlying cause of overexploitation and unsustainable management of essential oil-bearing plants. Peruvian Minthostachys spp. are pulled out from the roots with little sign of regeneration; and in Argentina, juvenile M. verticillata is harvested before flowering (Schmidt-Lebuhn, 2008; De la Cruz et al., 2014). The fact that these two countries are the primary producers of Minthostachys essential oil on a commercial scale is cause for concern. Other factors that negatively impact Minthostachys population numbers, as evidenced in Colombia, are fires, and the loss of natural habitat due to urbanization and monoculture (Schmidt-Lebuhn, 2008).
Collecting data on endemic population densities is critical to establish a baseline category for the conservation status of these plants. Also critical is providing education about the methods of sustainable harvesting, cultivation, and distillation methods. Consequently, plans are underway in southern Peru to assess population densities of Minthostachys spp., teach methods of sustainable harvesting and management, and to establish a high-quality source of Minthostachys essential oil for clinical research and integrated medicine in North America. Projects like these help to protect plant species, strengthen sometimes impoverished communities through monetary return, and preserve local knowledge of traditional medicine.
1susto: the body containing two different entities. Symptoms: chronic fatigue, sadness, and anxiety; uncontrollable crying; insomnia; depression.
2aire: strong and consuming energy from high altitutde. Symptoms: exhaustion; nausea; migraine; blurry vision; muscle and heart pain; sharp pain in lungs.
3mal aire/mal viento: the existence of a malevolent, destructive force or power that is transmitted through the air and wind.
4espanto: similar to 1susto but caused by a soul being lost due to fright rather than from sickness.
I’d like to thank Gabriel Mojay for his unwavering support, and his significant contributions including editing, designing and contributing data to Tables 1 and 2, preparing the Figures for submission, and for providing germane research articles. I’d also like to acknowledge Dr. Rosario Rojas for contributing research papers, Nicole Degagne for her work on the references, and the many people who graciously offered to provide me with their invaluable opinions and knowledge including Robert Tisserand, Victor Huaman, and Lin Ylla.
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This article is currently in press for the Spring 2018 International Journal of Professional Holistic Aromatherapy.