﻿AbstractBahianais expanded from 1 to 2 species with the description ofB.occidentalisK. Wurdack,sp. nov.as a new endemic of the seasonally dry tropical forests (SDTFs) of Peru. The disjunct distribution ofBahianawith populations ofB.occidentalison opposite sides of the Andes in northwestern Peru (Tumbes, San Martín) andB.pyriformisin eastern Brazil (Bahia) adds to the phytogeographic links among the widely scattered New WorldSDTFs. AlthoughB.occidentalisremains imperfectly known due to the lack of flowering collections, molecular phylogenetic results from four loci (plastidmatK,rbcL, andtrnL-F; and nuclear ITS) unite the two species as does gross vegetative morphology, notably their spinose stipules, and androecial structure. Spinescence inEuphorbiaceaewas surveyed and found on vegetative organs in 25 genera, which mostly have modified sharp branch tips. Among New World taxa, spines that originate from stipule modifications only occur inBahianaandAcidocroton, while the intrastipular spines ofPhilyraare of uncertain homologies.