Research update

In 2008, I published a review article summarizing the state of research on Minthostachys. It included an overview not only of systematics, taxonomy, morphology and anatomy, but also of results outside of my own expertise, such as biochemistry, pharmacology, ethnobotany and domestication. I also tried to apply a coherent taxonomy, and attempted to identify the study species of as many studies as possible. For the foreseeable future, this review will remain the perfect starting point to familiarize oneself with the state of the art. Nevertheless, time marches on, and additional studies have been published since, and I have even found a few older articles that I had missed in composing the manuscript. From now on, this new section of the website will be used to provide an update on Minthostachys research, assuming the aforementioned review as known.

Note that as far as possible, I will follow the taxonomy of my monograph of the genus irrespective of the names the authors of the individual studies use for their study plants. There are, for example, some Argentinean researchers who call their endemic species, the peperina M. verticillata, by the name M. mollis, following Epling & Játiva's (1963) suggestion to treat the genus as monotypic. Full references for the discussed articles can be found in the list of literature section of this website. If you know of additional articles that I should discuss here, or if you have even published one yourself, please contact me.

May 2010

Effects of the oil. González & Marioli (2010) found the decoctions of Minthostachys verticillata and Eucalyptus cinerea to the the most efficient of ten plants tested for their ability to inhibit the growth of Paenibacillus larvae, a bacterium threatening domesticated honey bees. The replication of Herpes simplex viruses is inhibited by extracts of the same species (Sabini et al., 2010). Antiviral activity of major components of M. verticillata oil - pulegone, menthone and limonene - has been demonstrated to occur at lower concentrations than those having a toxic effect on the treated cell lines in vitro (Vogt et al., 2010).

January 2010

Effects of the oil. Another test of the antioxidant capacities of plant extracts has been conducted by Dadé et al. (2009). Among the plants they examine is Minthostachys verticillata, but it was not found to be among the most efficient extracts.

Taxonomy. I have recently published a separate Spanish manuscript dealing only with the Bolivian representatives of Minthostachys (Schmidt-Lebuhn, 2009). It leaves out many pieces of information that were already presented in the monograph, but on the other hand it contains a few more details on distribution and ethnobotany I later learned from herbarium specimens at the botanical institutes of La Paz, Cochabamba and Santa Cruz that were not previously available to me. For example, M. ovata is now known to occur much farther to the South than before. It may also be useful for the Bolivian scientific community simply to have a country-level Spanish identification key available. The paper has appeared in the Revista de la Sociedad Boliviana de Botánica which unfortunately does not seem to have an online version. If you are a researcher interested in a reprint, please contact me.

October 2009

Ethnobotany. An ethnobotanical study in nine communities near Córdoba, Argentina, mentions the use of Minthostachys verticillata (called M. mollis in the paper) as a digestive, abortifacient and "to reduce pressure" (stress?) (Arias Toledo 2009).

Effects of the oil. Palacios et al. (2009) have tested the essential oils of nine plants, among them Minthostachys verticillata, for their insecticidal activity against the common house fly, and found it to be the most effective of the nine. This may have something to do with the fact that the principal component of the Minthostachys oil in their study was the toxic substance pulegone, comprising nearly 70% of the oil.

Domestication. At Córdoba, colleagues are searching for ways to take pressure from local populations of Minthostachys verticillata that are being overexploited, and to develop protective measures. A paper has just been published on the variability of plants grown from seeds (Ojeda 2009), but unfortunately I have not yet obtained a reprint, and there does not seem to be an online version of the journal. With this finely crafted link you should be able to see the content page of the issue but nothing more for the moment.

September 2009

Ethnobotany. Another paper that I found belatedly is a book chapter dealing with the uses of plants in Argentina (Juliani et al. 2007). The peperina Minthostachys verticillata is reported to be used in ca. 7% of the plant products that were examined, but in 50% of all examined composite yerba mate mixtures. Yerba mate is a cultural icon of Argentina, a tea-like drink that is consumed in large quantities.

Effects of the oil. Mora et al. (2009) have examined the essential oil of a Venezuelan Minthostachys and tested its antibacterial activity in vitro. They found the oil to be dominated by pulegone (55%) and trans-menthone (ca. 32%) and to have an inhibitory effect against various bacteria. Unfortunately, I have not found online access to the manuscript, only to its abstract, and can consequently not give a link to or more detailed information about the study. It was published in Natural Products Communications 4 (7), pages 997-1000.

Domestication. Another publication by the research group of Huanuco has become available (Maquera Lupaca et al. 2009). In this case, they have tested different cutting times in wild and cultivated accessions of Minthostachys mollis. They found that the growth of new shoots and leaves was most vigorous if the plants were cut at the start of flowering. Strangely and in contrast to a somewhat comparable study in Argentina (Bandoni et al. 2002), they did not find strong differences in the amount of essential oil at different times through the season. They also reported on the perception of the plants by the women of the local study area; two kinds of muña are differentiated, muña blanca for the use as a condiment and muña negra or muña macho as a medicinal plant and pest repellant. They are distinguished by the stem colour, probably related to presence or density of the indument.

July 2009

Ethnobotany. In an ethnobotanical study conducted by Thomas et al. (2009), a Minthostachys was found to be one of the most important medical plant species among Quechuas of Apillapampa, Departamento Cochabamba, Bolivia. The article calls the plant M. andina, based on a taxonomic mess-up that I discuss here (y aqui en Castellano). While I have not seen the voucher specimen that the authors have deposited in Bolivian herbaria, M. andina does not occur in their study area, and it is nearly certain that they have in fact dealt with M. ovata. It is mentioned that the plant has eight different medicinal uses, but no specifics are given.

Effects of the oil. Cariddi et al. (2009) have recently published a study on the antiallergic effect in vitro of Minthostachys verticillata oil on the cells of patients allergic to dust mites. The essential oil was also analyzed and found to consist of 63% pulegone, 16% menthone and ca. 2% limonene.

June 2009

Ethnobotany. A study of the traditional insecticidal and repellant uses of plants of Cajamarca, Peru, mentions the use of Minthostachys for the protection of stored tubers (Orozco & Lentz 2005), a practice that I have so far only read about with reference to southern Peru and Bolivia. Without giving specifics, the authors also mention use for the treatment of internal parasites in humans. They express dissatisfaction with the inconsistent results of a toxicity assay that was subsequently conducted, but caution that this could have been due to seasonal variability in essential oil content of the plants or an inadequate extraction process. Vouchers for the studied Minthostachys were deposited under the number Orozco 226 at both NY and CPUN. Unfortunately, I have not found them online so far and thus cannot verify their taxonomic affiliation; in the study area, both M. mollis and M. spicata can be found. Martínez (2005) studied the collection and sale of medicinal plants in the district of Santa María near Argentinean Córdoba. As should be expected for this area, Minthostachys verticillata (peperina) (called M. mollis in the paper) turned out to be the species consumed in the largest quantities. The plants are often collected by campesinos and sold dried or semi-processed to local buyers, sometimes even to tourists at roadside stands. Many campesinos apparently get by only selling this species, so high is its demand. The author even gives prices for the trade: the collectors receive 5-8 pesos per kg of dried peperina, while other herbs go for 3-6 pesos. Fresh peperina is worth only 3-4 pesos per kg. He estimates that the collectors thus receive between 17 and 80% of the final price of the products the herbs are processed to. He expresses concern about the fact that collection is nearly exclusively from wild populations and suggests further research on population sizes, domestication and protection measures. The primary use of peperina is given in this paper as a digestive. Commendably, the author deposited a voucher specimen at ACOR, but in this case the identity of the plant is clear as only one species of Minthostachys occurs in the area.

Conservation. As mentioned in the previous paragraph and other related articles, the Argentinean peperina (Minthostachys verticillata) is probably over-exploited at least in the Córdoba area. Martínez et al. (2006) suggest it as one of eight local species that should receive prioritized conservation measures based on questioning the collectors and sellers of medicinal herbs and the calculation of an index of conservation priority (ICP). It should be noted that the peperina even received the highest ICP of all ca. 84 (sometimes ill-circumscribed) taxa that were examined.

Effects of the oil. Ramos Llica et al. (2008) conducted assays to examine the andioxidant capacities of the extracts of several Peruvian medicinal plants, among them a Minthostachys. In contrast to the studies above, the authors do not give any details about the exact provenance of the plant material, let alone deposit and cite a voucher specimen, so that the taxonomic affiliation cannot be verified. It is, however, statistically most probable that their identification of the Minthostachys as M. mollis is correct unless the plants are from southern Peru, as M. mollis is by far the most frequent and widely distributed species of its genus in the central and northern parts of the country. The extract of this Minthostachys showed a strong (although in comparison to the other plant extracts and Vitamin C rather average) efficiency in capturing free radicals.

May 2009

Ethnobotany. Yerba maté is a traditional Argentinean drink similar to tea made from the leaves of the holly Ilex paraguariensis. Yerba compuesta is the same but with the addition of other aromatic herbs, among them sometimes the peperina Minthostachys verticillata. Scipioni et al. (2007) analyzed the composition of nine trademarks of yerba compuesta, three of which contained peperina. A completely different use of Ecuadorian Minthostachys was documented by Cavender & Alban (2009) who compiled a list of magical plants employed by traditional curanderos of the country. Apparently, the aromatic plant is meant to help against "mal aire", "mal viento" (both relatively ill-defined illnesses thought to stem from harmful spiritual influences) and "espanto" (horror) if brushed against the body of the patient.

Effects of the oil. Maldonado et al. (2007) compared the effect of Minthostachys verticillata oil and leaf decoctions (and decoctions of another plant) on the degranulation of basophiles of allergic patients to that of several antiallergic drugs in vitro. Combinations of some of the standard drugs were most effective, but the natural products also led to a significant reduction in the allergic reaction. The oil of M. verticillata used in the study was found to be very rich in pulegone (over 60%) and menthone. Another interesting aspect of Minthostachys is the suppression of potato sprout growth and tuber rot by its oil. Andean farmers have traditionally kept potato and oca tubers fresh by storing them between layers of the aromatic leaves of these and related plants. An article examining this effect is that of Coleman et al. (2001), who stored potato tubers for up to two months in an atmosphere saturated with different oil components. They found no adverse effects of the menthone treatment on sugar content of the tubers. Menthone and isomenthol were much more efficient sprout suppressors than carvone.

April 2009

The first update will probably be the longest ever, as I have to get numerous publications out of the way that I have discovered since the review article was printed.

Ethnobotany. Already in 1998, Hammond et al. reported the tradional uses of Minthostachys mollis in an area called the Callejón de Huaylas (Dep. Ancash, Peru). They wrote that an "infusion of the leaves is drunk or whole leaves eaten as a vegetable to treat digestive ailments and as an anthelmintic and an aphrodisiac". An ethnobotanical survey mentioning the peperina, Minthostachys verticillata, has been published by Consolini et al. (2007). In the present case, the authors examined the sale of medicinal plants in pharmacies of the Buenos Aires province. Even though the peperina does not occur in that area, it is prescribed as a diuretic. The peperina was also one of the plants mentioned in a long-term study on the medicinal plants of the Sierra de Comechingones, Argentina (Goleniowski et al. 2006).

Essential oil composition. Two Peruvian researchers have examined the essential oils of plants from three areas of their country: Tarma, Huaraz and Huancavelica. Judging from this provenance, the study species was most likely Minthostachys mollis. As often, the oils were rich in menthone and pulegone, but the most important component in the oil from Tarma was, unusually, 1-tetradecene (Fuertes & Munguía 2001). Unsurprisingly, several research groups based in Argentinean Córdoba, which could be called the world capital of Minthostachys consumption, are conducting research on the local species called peperina. One of them is particularly interested in the economically relevant changes in the oil composition induced by herbivory. Two of their articles from 2005 have already been discussed in the review. A third article observes an increase of the toxic component pulegone after damage from a leaf miner (Banchio et al. 2006).

Effects of the oil. In 2006, Alonso-Amelot et al. examined the inhibition of germination of various plants by oil of a Venezuelan Minthostachys. The essential oil of the study plants was extremely rich in pulegone - more than 80%. Cariddi et al. (2006) have added another study on the inhibition of allergic reactions by essential oil of M. verticillata. At the IX Simposio Argentino y XII Simposio Latinoamericano de Farmacobotánica in 2007, Vogt et al. presented results from their work on the growth inhibition of fungi of the genus Fusarium by M. verticillata oil extracts. At the same conference, Gleiser et al. (2007) presented a similar study on the insecticidal activity of the oil against mosquitos. Even though the latter called their study plants M. mollis, they should also be the Argentinean species M. verticillata. In an evaluation of twelve aromatic Argentinean plants, M. verticillata showed intermediate repellent activity against mosquitoes (Gillij et al. 2008). Cano et al. (2008) have published a study on the antimycotic effects of M. mollis - in this case most likely the real thing, judging from the provenance of the samples. The essential oils were also analyzed, and were found to be dominated by pulegone and menthone.

Domestication. The Peruvian Universidad Nacional Hermilio Valdizán of Huánuco has a research group that is interested in the domestication and conservation of Minthostachys. Their article on the optimal spacing of cultivated plants has already been discussed in the review. In the meantime, they have published another study in their university's journal (Maquera Lupaca et al. 2008), this time examining the effects of spacing together with fertilization. Results indicate that application of fertilizer increases the size of the plants, but does not lead to more branching. At the same time, there was a high fluctuation between individual plants. The study plants most likely belong to the species M. mollis. Another paper from the same researchers on the optimal harvesting time is in press and will be discussed as soon as available.

Morphology. The last publication that I found for this month is a bit unusual. Scandaliaris et al. (2007) wrote a paper to tell us that there are two aromatic Lamiaceae sold under the common name peperina: Minthostachys verticillata (they sink it in M. mollis, however, following Epling & Játiva, 1963) and Calamintha nepeta, and how to distinguish them. The first piece of information is not very surprising, considering that common names are notoriously applied in a very imprecise manner. Some colleagues from Halle University, for example, recently kept their eyes open for me when they went to the Córdoba area, and they were shown a third species, a Clinopodium in that genus' current circumscription, that was also called peperina by the locals. On the other hand, it should not be necessary to produce a nine pages long paper with extensive morphological descriptions to be able to differentiate a Calamintha and a Minthostachys. There are other genera that are much more similar to the true peperina, like the aforementioned Clinopodium. In addition, the descriptions in the article are not precise enough to exclude the possibility that the authors are dealing with Calamintha sylvatica instead of C. nepeta. Still, it is rare that Minthostachys is examined morphologically at all, considering that people are usually only interested in the essential oils, and the publication does feature some nice drawings.