Monophyly and phylogenetic relationships of Minthostachys (Labiatae, Nepetoideae) examined using morphological and nrITS data

Minthostachys (Benth.) Spach (Labiatae) from Andean South America was long held to be closely related to Macaronesian Bystropogon L’Hér. or to North American Pycnanthemum Michx. The possibility of a close relationship to elements of South American Satureja/Clinopodium s.l. is here proposed for the first time, and a phylogenetic analysis of nrITS data is employed to test the competing hypotheses. For Minthostachys and its putative closest relatives, the possible evolution of morphological characters is investigated with a cladistic analysis. The results suggest that Minthostachys is nested in a clade of South American Mentheae, and probably in the former genus Xenopoma Willd., a group of small-flowered, bee-pollinated species currently included in Clinopodium L.. Minthostachys is considered monophyletic based on nrITS data and its scandent habit.