## 3 Discussion
 & 13 June 2020 & \(44^{\circ}47^{\prime}46.15^{\prime\prime}\) N & \(13^{\circ}54^{\prime}25.96^{\prime\prime}\) E & Cfa 2 \\
21 June 2020 & \(43^{\circ}10^{\prime}12.71^{\prime\prime}\) N & \(17^{\circ}11^{\prime}45.75^{\prime\prime}\) E & Csa 3 \\
21 June 2020 & \(43^{\circ}40^{\prime}44.79^{\prime\prime}\) N & \(15^{\circ}57^{\prime\prime}41.25^{\prime\prime}\) E & Csa 3 \\
21 June 2020 & \(43^{\circ}10^{\prime}13.3^{\prime\prime}\) N & \(16^{\circ}40^{\prime}24.45^{\prime\prime}\) E & Csb 4 \\
21 June 2020 & \(43^{\circ}55^{\prime}1.51^{\prime\prime}\) N & \(16^{\circ}28^{\prime}8.41^{\prime\prime}\) E & Cfb 5 \\
21 June 2020 & \(43^{\circ}31^{\prime}13.56^{\prime\prime}\) N & \(16^{\circ}36^{\prime}10.44^{\prime\prime}\) E & Cfa 2 \\
21 June 2020 & \(43^{\circ}55^{\prime}1.51^{\prime\prime}\) N & \(16^{\circ}28^{\prime}8.41^{\prime\prime}\) E & Cfb 5 \\
21 June 2020 & \(43^{\circ}31^{\prime}13.56^{\prime\prime}\) N & \(16^{\circ}36^{\prime}10. Clear separation between _S. montana_ and _S. romana_ samples was observed in the PCA with both fiber types used, with _S. romana_ M showing a distinct VOCs profile. Observed differences in the chemical composition of investigated Croatian _Sideritis_ species from previously published data on VOCs composition of aerial parts from samples of different geographical origins may be explained by different ecological conditions (Table 4). According to Koppen climate classification [45], the collection areas from which the populations included in the present study were sampled belong to different climates including the Mediterranean climate with hot summer (_S. romana_ B, _S. romana_ M), the Mediterranean climate with warm summer (_S. romana_ from Praznica (_S. romana_ P)), the temperate humid climate with hot summer (_S. romana_ K, _S. montana_ M) and the temperate humid climate with warm summer (_S. montana_ J). This might have party affected their VOCs production. As it is known, VOCs composition can change depending on the type of stimulus received from the environment [32]. For example, variation of VOCs content may have been caused by environmental stress such as drought stress, as it was detected in the study of different cultivars of _Thymus vulgaris_ L., in which \(\alpha\)-phellandrene, \(o\)-cymene, \(\gamma\)-terpinene and \(\beta\)-caryophyllene were recognized as the compounds included in drought stress adaptation [48]. These compounds were observed as one of the major identified VOCs in the present study. For example, \(\gamma\)-terpinene was found to be especially dominant in _S. romana_ M. Additionally, individual VOCs production might have been affected by the plant species that grew in the vicinity of investigated specimens in each habitat (place of collection) [49; 50]. Although this has not been recorded in the present study, insight into the diversity of plant species in the harvesting locations can be partially gained through floristic studies that were conducted in the areas that are overlapping with or are near to the harvesting locations [51; 52; 53; 54; 55; 56; 57; 58; 59]. Besides ecological conditions, the observed differences may also be explained by the applied methods of extraction, having in mind that none of the previously mentioned studies used the HS-SPME method for extraction of VOCs from _S. romana_ and _S. montana_. Instead, as already mentioned above, most authors used hydrodistillation, with the exception of the study done by [PERSON] et al. [27], in which steam distillation was used. A few comparative analyses of plant volatile compounds isolated by hydrodistillation and HS-SMPE were published. A study on _Myrtus communis_ L. showed that the applied microextraction techniques (HS-SPME and HS-SDME) extracted compounds that were more volatile, such as \(\alpha\)-pinene and limonene, in comparison to hydrodistillation, which, in turn, obtained higher peak areas for low volatile compounds [60].