What is Minthostachys? (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.

Overview

Minthostachys is a shrubby genus of the mint family (Lamiaceae) inhabiting the Andes from Venezuela to Argentinian Córdoba. It is of considerable ethnobotanical, pharmaceutical, and economical interest because of the aromatic oils found in glands on its leaves and stems. Traditionally, people collect the plants for tea, as a condiment, or for medicinal uses, and in Argentina and Peru Minthostachys oil is produced on a larger scale.

Despite this, the genus as a whole had last been taxonomically and systematically studied in 1936, and consequently our knowledge of this interesting plant group was severely outdated until a new study was conducted in 2002-2005.

Names

The genus is known to the local population under various names, the most important including Muña (especially central Peru to Bolivia), Peperina (Argentina), Poleo, Tipo (both Ecuador), and Chancua (northern Peru). It should be noted that people usually do not differentiate between different species, and that even other genera of the same plant family, like Clinopodium or Hyptis, are identified with the same names. Similarly, Minthostachys is sometimes called Menta, Oregano, or Toronjil.

Being in its distribution restricted to South America, Minthostachys has no proper English name. The scientific name could be roughly translated as "mint-spike".

Distribution and Ecology

The genus is distributed from the Venezuelan states of Monagas and Sucre in the north-east along the coastal cordillera to the Andes and then south through Colombia, Ecuador, Peru, and Bolivia to around Córdoba in Argentina. It colonizes preferably open or disturbed areas, often land-slides, but with very different hydrological conditions. Some species predominantly inhabit cloud forests or similar moist, forested environments, and others are predominantly found on dry to very dry, sandy to rocky slopes. The elevational amplitude of Minthostachys ranges from 500 m, especially at the northern and southern limits of its distribution, to up to ca. 4200 m in the central part.

Recognizing Minthostachys

The plants are aromatic, scandent shrubs up to 3 m tall. The leaves are decussate, entire, usually 2-5 cm, sometimes up to 10 cm long, and nearly always serrate. The flowers are quite small and arranged in usually dense pseudowhorls. The calyces (magnifying glass!) are 2-5 mm long, bilabiate, and have 13 veins - the three teeth of the upper calyx lips share seven veins while each of the two teeth of the lower lip has three veins. The corollas are white, often with lilac nectar guides.

The following other plants are frequently confused with Minthostachys:

Some species of Hyptis appear similar at first sight. However, those occurring in the Andes are mostly herbaceous and many have entirely lilac flowers; more importantly, the calyces are quite different from the description given above.

Clinopodium gilliesii [= Satureja parvifolia] and relatives are a small group of species with a similar general habit but which can be differentiated by the very small leaves and flowers whose calyces are also actinomorphic.

Clinopodium cylindristachys [= Satureja cylindristachys] of northern and central Peru is very easy to confuse with Minthostachys due to the small flowers and similar aromatic scent but differs in the lack of bracts in the greater part of the long, slender inflorescences (vs. always present though often reduced in size).

Clinopodium vanum [= Satureja vana] is one of the most similar species of South American Clinopodium, but has distinctively larger flowers (ca. 10 mm vs. up to 7 mm) of which there are fewer per pseudowhorl, and the calyces are also less bilabiate. Also related is Clinopodium bolivianum with much smaller leaves and larger flowers than found in Minthostachys.

Especially in certain parts of Argentina, introduced Calamintha sylvatica (or C. nepeta) can be confused with the native species of Minthostachys. This mistake is somewhat understandable because both are known and sold under the same common name, and both plants have petiolated cymes and similar aromatic scent. Helpful characters for differentiation include the much larger flowers, more obviously bilabiate calices with strikingly longer lower teeth and the smaller leaves of the Calaminthas in comparison to M. verticillata.