A new species, S. tricae D. Hunt, and new sectional names in Selenicereus (A. Berger) Britton & Rose are proposed. The name S. sect. Salmdyckia D. Hunt is proposed for the species hitherto referred to Mediocactus B. & R., since neotypification of Cereus coccineus Salm-Dyck ex De Candolle renders the name Mediocactus a synonym of Heliocereus B. & R. S. rizzinii Scheinvar is treated as a synonym of S. setaceus (‘Mediocactus coccineus’ auctt.). Reasons for recognizing two species only in Aporocactus Lemaire are given and Lemaire's etymological explanation for the generic name re-stated.