The genera Espostoa, Pseudoespostoa, Thrixanthocereus and Vatricania occur in western South America (Ecuador, Peru, Bolivia) and bear prominent lateral cephalia. Because it had been suggested that they should be combined into the single genus Espostoa, their anatomy was studied for clues as to the closeness of their relationships. In general they all resemble each other strongly, and although each has a number of unusual features, each usually shares some of those features with other members of the group so none is truly unique. There is no anatomical basis for maintaining them as separate genera. Many of their unusual features are shared with Weberbauerocereus, Haageocereus, Trichocereus and several related genera, but the anatomy of these groups is not known well enough to be certain of any phylogenetic relationship with the Espostoa group.