Some notes on the species of Minthostachys and their names (repost from old website)

I am considering to retire my Minthostachys website, but it would be good to have some of the information still available on the internet. The genus is, after all, of some cultural and economic significance to the people of the Andes. This is therefore one of a series of posts transferring previously written texts from the aforementioned website. Please disregard unless you are interested in this particular genus.

Some names are misapplied particularly often in the scientific literature, so I want to take some time to use this page to make special reference to theses cases. It is important to note that most of these cases are not matters of opinion. It may (arguably) be a matter of opinion whether to recognize several local species in Minthostachys or whether you find it preferable to recognize only one extremely variable species, depending on the species concept that is applied. I like to think that other botanists, faced with the same data and study material, would have arrived at a very similar taxonomic treatment and also recongized several different species as I did, and it could be noted that my approach is quite similar to that of the previous treatment of the genus (Epling 1936), where several important species such as Minthostachys acutifolia, M. ovata or M. spicata were circumscribed in the same way. Nevertheless, some colleagues would maybe have preferred to lump the whole genus into one species. Be that as it may, the important issue here is that it is most certainly not a matter of opinion what name you use, for example, for the study plant in your ethnobotanical survey or analysis of essential oil content, or for the plant of which you are offering seeds for purchase.

Taxonomy, the science of naming organisms, is meant to serve our communication by creating a set of rules for the consistent and logical application of names. This allows the target audience of your published scientific study to be sure what plant you actually examined, making your study reproducible and comparable, important aspects of good scientific practice. Likewise, it allows the purchaser of a plant to be sure that she gets what it says on the label. Following the rules of taxonomy, those who recognize only one species in the genus Minthostachys must call it M. mollis (HBK) Griseb., as the specific epithet mollis is the oldest that has been published and thus has priority over the names of species that are lumped together with it but were described later. Consequently, researchers have it relatively easy if they call their study plants M. mollis and leave it at that, as they could simply retreat to the position that they regard the genus to be monotypic. However, many colleagues, including myself, would argue that it makes eminent sense to recognize the morphologically, ecologically and geographically diverse forms of Minthostachys as separate species, and so it is not surprising that we find many scientific publications where the study plants are variously called M. andina, M. setosa, M. verticillata, etc. Now, how do we decide what name applies to a certain plant that we have in front of us?

From a taxonomist's perspective, we first have to identify which species to recognize and how to distinguish them based on the samples that are available for study. Once this is accomplished, we need to put names on the groups of samples that we want to recognize as distinct. Whenever a species was described as new to science and given a name, a sample was designated as the type specimen of that name. A taxonomist will now see if existing type specimens can be assigned to the species she wants to recognize. If exactly one type can be assigned to a particular species, then the name of which it is the type (usually) is the accepted name of that species. If more than one type is assigned to the same species, the oldest name (usually) has priority, others become so-called synonyms and should not be used. If no type specimen belongs to a species, it can be described as new to science. Now, obviously we have several potential pitfalls here, and it just so happens that we can observe some of them in the case of Minthostachys. For example, it is possible that a species was happily but mistakenly called by a certain name for decades, but now our taxonomist finds that the type specimen that this name is affixed to in fact unequivocally belongs to another species. Unfortunately, there is nothing we can do about this; the rules of taxonomy and the interest in unambiguousness precede the interest in continued use of a misapplied name. This explains some of the issues that will be discussed shortly.

From the end-user's perspective, a researcher who is only interested in identifying the plant so that she knows what she just fed into her mass spectrometer has two options. Either she can take a plant sample (or maybe even a decent photograph) to a colleague specializing in the local flora or the plant group in question, or she can pick up a flora or monograph herself. The first approach relies on the expertise of the colleague who, if you are unlucky, may make a mistake or base the identification on outdated information. The second approach is dependent on whether the book that is being consulted is up-to-date and comprehensibly written. In the case of Minthostachys, no taxonomic work was conducted between 1936 and 2002, while in the meantime countless ethnobotanical, biochemical, pharmaceutical and agricultural studies examined members of the genus. In addition, Carl Epling's synopsis from 1936 was published in a journal that is not easily available in many Latin American institutions, it contained descriptions of only some of the recognized species, and it featured no drawings or photos. It should come as no surprise that over the decades this has lead to a number of misidentifications of study plants as well as to a number of misconceptions about the correct names.

These are now the cases that should be kept in mind when reading studies of Minthostachys, looking at labelled specimens or trying to identify new material:

1. It seems that over the years, it unfortunately became customary in Bolivia to apply the name Minthostachys andina to the hairy highland species of Cochabamba, Sucre and Potosí. Several publications give this name to their study species. However, neither the aforementioned treatment by Epling nor the type specimens leave any doubt that the name M. andina (Rusby ex Rusby) Epling does not apply to this species, but to another one, that with the smallest leaves of the whole genus. It occurs only in the vicinity of Sorata north of La Paz and nowhere else. The Cochabamba species and most likely study plant of the Bolivian publications must rightfully be called M. ovata (Briq.) Epling. Both species look quite different and are easily distinguished.

2. A particularly unfortunate case is that of the dominant species of the southern Peruvian highlands. It is quite glabrous (hairless), relatively slender-leafed, typically very sharply aromatic and tends to have curved-spreading calyx teeth, so it is comparatively easy to recognize and delimit from other species. For some reason, Epling consistently used the name Minthostachys glabrescens (Benth.) Epling for this taxon, as shown by his writings and his annotations of herbarium specimens. Closer examination of the type specimen of that name, however, reveals that it differs in several important characters. Its geographic provenance should also have been a hint: it was collected not in southern Peru, but in Ecuador - the true M. glabrescens is a local endemic of the Loja area and maybe adjacent parts of northern Peru. The dominant southern Peruvian highland species had, in turn, never received a scientific name. In my monograph, I have named it M. acris Schmidt-Leb.; the specific epithet means "sharp" and refers to the strong minty scent.

3. Minthostachys tomentosa (Benth.) Epling was recognized as a distinct species in the northern Andes even though even Epling mentioned that it was scarcely separable from M. mollis. After the examination of many specimens, I have come to the conclusion that its recognition does not make any sense at all, and have reduced it to a synonym of the latter.

4. There exists a certain degree of confusion with regard to the naming of Minthostachys from Argentina. As outlined above, the correct name depends on the species concept that is applied. If several species are recognized in the genus, only one of them occurs in Argentina, and it also seems to be restricted to that country; its correct name is M. verticillata (Griseb.) Epling. If all species are lumped into one, this one remaining species is called M. mollis (HBK) Griseb. Some Argentinean researchers use the first approach, others the second.

Reference

Epling CC, 1936. Synopsis of the American Labiatae. Repert. Spec. Nov. Regni Veg. Beih. 85.