Taxonomic approach of the species Thymus sibthorpii Bentham: distribution, morphology and essential oils in different habitat types (in Greek)

The present study consists of four parts concerning the: (i) taxonomic history of “thyme” plants, (ii) geographical distribution of Th. sibthorpii in Greece, (iii) morphological as well as (iv) chemical (essential oil content) variation of Th. sibthorpii growing wild in different habitat types. The overall results are discussed in relation to the taxonomic implications within the sect. Serpyllum. The first part is focused on the nomenclatural and morphological relationships of the nowadays known taxa of the genus Thymus L. to the: (a) polynomials mentioned in the early botanical works of the 16th to 18th century and (b) plant drawings and descriptions included in antiquity herbals, with emphasis on those based on the work of Dioscorides “Materia Medica”. Results suggest that genus Thymus is related with the pre-Linnaean group of polynomials Thymum and Serpyllum as well as the descriptions of the plants “thymos” and “erpyllos” as included in “Materia Medica” recensions. The overall study of characters suggests a shift in the type of characters used during pre- and post-Linnaean periods. In particular, vegetative macro-morphological characters are gradually enriched with or replaced by reproductive micro-morphological characters in recognizing new taxa. On the basis of this change new Thymus taxa from E Mediterranean were described, including Th. sibthorpii. In the second part, the analysis of Natura 2000 database and Th. sibthorpii herbarium specimens support three different habitat types as the most common for Th. sibthorpii populations, which occur in five floristic regions of Greece (i.e. NE, NC, EC, SPi and NAe). In the third part a total of 34 morphological characters of Thymus sibthorpii plant individuals are measured on plants collected from wild growing populations of six different habitat types. The variation of 28 characters is related to the habitat type where the plants were collected. The findings indicate that different habits of plants are related to the habitat types. Plants of Th. sibthorpii from different areas and habitat types were compared against herbarium vouchers of closely related taxa. Results suggest high morphological resemblance between the different Th. sibthorpii habits and specimens belonging to the species Th. heterotrichus Griseb., Th. comptus Friv. and Th. degenii Heinr.Braun. Consequently, four species, Th. sibthorpii s.str., Th. heterotrichus, Th. comptus and Th. degenii are herein proposed to be included under the group Th. sibthorpii s.lat. Finally, measurements (by hydrodistillation) of the essential oil content of leaves and inflorescences of single Th. sibthorpii plant individuals revealed a range between 0,2% and 3,5% (mL 100 g-1 dry weight). Furthermore, the essential oil content of individual plants is found to be related to the habitat type. Mean diameter and density of peltate glandular hairs can be used as an index of the essential oil content of leaves and inflorescences of Th. sibthorpii plant individuals.