Variation in Mentha arvensis L. (Labiatae). I. The North American populations

Abstract

Most North American populations of Mentha arvensis differ from those in Europe in leaf and calyx characters, but the extremes of variation overlap. However the former have a diploid chromosome number of 96 and the latter 72. The North American populations are morphologically very variable and much of this variation is genotypic. However, none of it is discrete and, as it shows little geographic or ecological coherence, taxonomic recognition appears undesirable. The following chemical races based on essential oil composition, occur in North America: Type 1–high in pulegone, isomenthone and menthone. Type 2–high in linalool, cfr-ocimene and trans-ocimene. Type 3–high in cw-isopulegone and fnmi-isopulegone. Type 4–high in cis- and trans-ocimene and in 1,8-cineol. These four chemotypes are not correlated with any of the morphological variations. The recognition of chemical races is discussed and it is concluded that where possible they should be based on diagnostic components, rather than on quantitative differences or the mere presence or absence of given compounds. The literature relating to biosynthesis and essential oil composition in Mentha arvensis is reviewed.