This is by far the largest section, even as to its range, which is about the same as that of the genus, with a clear centre of diversity ranging from north-eastern Mediterranean countries to the Caucasus and adjacent highland areas. Morphologically, it shows closest relations with sect. Hyphodromi, and at least two different lines can be shown connecting these two sections, one between the North African central group of Hyphodromi and Balkan members of subsect. Isolepides, and the other between the former (Thymus syriacus Boiss.) and subsect. Kotschyani.
The European members of sect. Serpyllum, as well as most, if not all, of its African and Asiatic representatives, can be divided into seven subsections. However, this system must be regarded as a working hypothesis-although seemingly working well so far-rather than as a final product of all-round study.