Analysis of DNA sequence data was used to clarify the circumscription and relationships of the small Mexican genus Asanthus. Results from non-coding regions, including the nuclear ITS and the chloroplast psbA-trnH spacer showed that Asanthus is clearly monophyletic and distinct from Steviopsis and Brickellia, two genera with which it is sometimes lumped, as well as from the closely related Brickelliastrum and Carminatia. The DNA sequence data also agree with morphological observations in showing that Asanthus is composed of three species, A. thyrsiflorus from the Sierra Madre Oriental and A. squamulosus and A. solidaginifolius from the Sierra Madre Occidental. Samples from the southern Sierra Madre Occidental that have been identified as A. thyrsiflorus are suggested by the presence of an additive pattern of polymorphisms in the nuclear ITS region to be of interspecific hybrid origin between A. thyrsiflorus and A. solidaginifolius, which is consistent with reports of their morphological intergradation in this area. The results suggest that geographic separation and divergence within Asanthus is now being followed by secondary contact, and point to a dynamic pattern of movement and change in the genus.