Micromorphological traits and essential oil contents of Micromeria kerneri Murb. and M. juliana (L.) Benth. (Lamiaceae).

Abstract

The chemical composition of the essential oil (analysed by GC and GC-MS), the types and distribution of trichomes and pollen morphology (analysed by scanning electron microscopy) were investigated in two closely related species, Micromeria kerneri Murb. and Micromeria juliana (L.) Benth. (Lamiaceae) from Southeast Europe as a contribution to their taxonomy. The essential oil of M. kerneri was characterized by a high concentration of oxygenated sesquiterpenes, with caryophyllene-oxide as the major compound. Caryophyllene-oxide was also the major component of the essential oil of M. juliana from all localities, except from Mt Krivošije (Montenegro), where piperitone oxide was the major constituent. Non-glandular trichomes, peltate trichomes, and two types of capitate trichomes (type 1 composed of one basal epidermal cell, and one head cell with subcuticular space; type 2 composed of one basal epidermal cell, two stalk cells, and one head cell with subcuticular space) were observed on leaves, the calyx and on the stem. Pollen of both species had six apertures (hexacolpate) set in the equatorial pollen belt (zonocolpate) and showed medium reticulate ornamentation. Multivariate analysis (PCA and UPGMA) of essential oil components clearly separated the investigated M. kerneri and M. juliana populations, and confirmed the opinion that they are different taxa. On the other hand, micromorphological traits between these species were the same. Nevertheless, definitive conclusions about the taxonomic relationships among these species will require genetic analysis.