The genus Cyclotrichium, a member of the tribe Mentheae subtribe Menthinae (Lamiaceae, Nepetoideae), was analysed with respect to morphological revision, phylogenetic analysis, and cytogenetic properties. All species of the genus were investigated for morphological characters and ITS (internal transcribed spacers) of nrDNA sequence comparison (except C. hausknechtii for ITS). Six members of the genus were also analysed for chromosome numbers. The combined results strongly suggested that Cyclotrichium is a separate genus in Nepetoideae with distinct morphological, phylogenetic, and cytogenetic characteristics. For intrageneric phylogeny of Cyclotrichium, 3 groups were recognised: 1. C. niveum; 2. C. origanifolium; and 3. the remaining 6 species. Clinopodium s.l. and Mentha appear to be most closely related to Cyclotrichium. The phylogenetic relationship of Cyclotrichium with Clinopodium s.l., Mentha, Micromeria, Melissa, and Satureja is discussed. This is the first report on the somatic chromosome numbers of 6 Cyclotrichium species and phylogenetic analysis of Cyclotrichium based on (nrDNA) ITS sequences.

The genus Cyclotrichium, a member of the tribe Mentheae subtribe Menthinae (Lamiaceae, Nepetoideae), was analysed with respect to morphological revision, phylogenetic analysis, and cytogenetic properties. All species of the genus were investigated for morphological characters and ITS (internal transcribed spacers) of nrDNA sequence comparison (except C. hausknechtii for ITS). Six members of the genus were also analysed for chromosome numbers. The combined results strongly suggested that Cyclotrichium is a separate genus in Nepetoideae with distinct morphological, phylogenetic, and cytogenetic characteristics. For intrageneric phylogeny of Cyclotrichium, 3 groups were recognised: 1. C. niveum; 2. C. origanifolium; and 3. the remaining 6 species. Clinopodium s.l. and Mentha appear to be most closely related to Cyclotrichium. The phylogenetic relationship of Cyclotrichium with Clinopodium s.l., Mentha, Micromeria, Melissa, and Satureja is discussed. This is the first report on the somatic chromosome numbers of 6 Cyclotrichium species and phylogenetic analysis of Cyclotrichium based on (nrDNA) ITS sequences.