This study presents the results of our comparative evaluation of diagnostic morphological characteristics of raw material from 11 species of genus Thymus L. of medicinal and raw material importance occurring in Ukraine. The following taxa were evaluated: T. serpyllum L., T. odoratissimus Mill. (T. glabrescens Willd.), T. borysthenicus Klokov & Des.-Shost., T. pallasianus Heinr. Braun, T. moldavicus Klokov & Des.-Shost., T. calcareus Klokov & Des.-Shost., T. alpestris Tausch ex A. Kern., T. × dimorphus Klokov & Des.-Shost., T. pannonicus All. s.l. (including T. marschallianus Willd.), T. pulegioides L. and T. roegneri K. Koch (T. alternans Klokov). Among wild species of thyme, only raw material of Thymus serpyllum is officially allowed for use with the purpose for production of pharmaceuticals and medicines. A comparison of the main characteristics is particularly important in view of the fact that raw material is represented by parts of plants (stems, leaves and flowers), which makes any whole comparison of species hardly possible. This study has revealed that stem pubescence, calyx structure, configuration/arrangement and type of leaf venation can provide valuable information for diagnostics of raw material of Thymus species. The results exhibited that according to characters of stem pubescence, calyx structure, shape and size of leaves the most similar are raw material samples of T. serpyllum and T. moldavicus. However, these species are rather well separated geographically, so the possibility of mixing of their raw material is negligible. Other species have significant morphological differences in certain characteristics by which they can be diagnosed in the raw material.
