Leptocereus is an Antillean genus of thin-stemmed cacti with 17 described species. We carried out a phylogenetic reconstruction with plastid DNA sequence data and a combined analysis with a set of 39 morphological characters using Maximum Likelihood and Bayesian inference criteria to explore the monophyly of the genus. We further analyzed the evolution of eight morphological characters to interpret the circumscription of Leptocereus and test for putative synapomorphies for the clade. Five plastid markers ( trn L-F, trn Q- rps 16, psb A- trn H, pet L- psb E, and rpl 16) were sequenced for fifteen species of Leptocereus , seven species of the related genera ( Armatocereus, Dendrocereus, Strophocactus ) and ten species from Hylocereeae, Pachycereinae, Stenocereinae were used as outgroup taxa. Our phylogenetic analyses suggest that Leptocereus is paraphyletic with a clade of the two Dendrocereus species nested within it. All Cuban species constitute a monophyletic group, as do the species of Hispaniola and Puerto Rico, which are sister to the Cuban clade +  Dendrocereus clade. No morphological character analyzed here was synapomorphic for the genus, but sunken areoles in the depressions of the ribs were a character present in all subclades of Leptocereus . Based on our molecular data and extensive fieldwork, a new circumscription of Leptocereus is proposed, which includes three new combinations ( Leptocereus albellus comb. et stat. nov., L. nudiflorus comb. nov., L. undulosus comb. nov.).