A new combination, Deinandra peninsularis (Moran) B. G. Baldwin, comb. nov., is proposed for D. greeneana subsp. peninsularis of Baja California, Mexico, a taxon that does not belong within D. greeneana, based on recent molecular and cytogenetic work. New chromosome counts for D. peninsularis and D. streetsii and previously reported counts for the other 20 species of Deinandra indicate that all perennial or facultatively perennial taxa of the genus share the modal, and probably basal, chromosome number of 2n  =  12_II. A new chromosome count for another member of the tarweed tribe, Arnica mallotopus [≡ Mallotopus japonicus] (2n  =  19_II), in Arnicinae, strongly contrasts with an earlier (somatic) count for that species (2n  =  18), which is often treated in a different genus based in part on the previously reported chromosome number.