We describe Serpocaulon psychotrium, a new species from northern South America, and provide for it a discussion of similar species, line drawings, field photographs, and a distribution map. It is often confused with, and probably related to, the species commonly called S. caceresii, also widespread in South America. We reinterpret S. caceresii as a heterotypic synonym of S. articulatum, an older name, and review the nomenclature of that species. Also, we provide a list of representative specimens for both species and a key to all pinnate species of Serpocaulon.