Ipomoea series Tyrianthinae (House) D.F. Austin is revised in light of recent systematic surveys of New World morning glories. The group includes two species of vines and three highly derived shrubs. Four varieties of I. orizabensis (Ledeb.) Pelletan are recognized for the first time; two are new to science, I. orizabensis vars. austromexicana and novogaliciana, and one requires a new combination, I. orizabensis var. collina (House) J.A. McDonald. Molecular studies indicate that Ipomoea ser. Tyrianthinae shares close phylogenetic affinities with Ipomoea sects. Calonyction and Tricolores, yet few morphological features support this arrangement. It is assumed, therefore, that highly derived elements of the tyrianthina complex have undergone rapid morphological change in the arid environments of central and northern Mexico.