Glandular Trichomes and Essential Oils of Mentha requieni Benth.

Distilled oils from leaves of Mentha requieni Benth. (2n=18)were analyzed by means of GC/MS. The essential oil consisted almost exclusively of the monoterpene ketones pulegone (79 percent)and menthone (14 percent). Leaf glandular trichomes were observed and counted by means of scanning electron microscopy (SEM)and data were subjected to analysis of variance (ANOVA)in order to verify significance of differences in densities and total number of trichomes between the upper and lower leaf epidermises. Abaxial and adaxial surfaces of M. requieni leaves possessed both peltate and capitate hairs, the latter present at densities always higher than those recorded for the peltate hairs. Nevertheless, M. requieni peltate hair density was high, if compared with that of other Mentha species. This resulted in a capitate/peltate ratio of 1.74, a value very uncommon for the genus, especially in the case of the upper epidermis. The chemical profile of the oil was discussed in relation to the taxonomic position of this rare Mediterranean endemic species. A strong morphological adaptation to the coastal environment could be envisaged in the reduced leaf dimensions and related trichome distribution.