The internal transcribed spacer (ITS) region of 18S-26S nuclear ribosomal DNA (nrDNA) in 36 species of Pinguicula(Lentibulariaceae) in Mexico and Central America, most of which are endemic to Mexico, was sequenced. Based on the ITS results, those species of Pinguicula studied were divided into three clades. In general, these cledes do not agree with the current conventional classification proposed by various authors except for Clade I. Clade I includes only two species belonging to section Isoloba, which are widely but sparsely distributed in Mexico and Central America. Clade II included 18 species, which have been conventionally classified in the sections Heterophyllum (six species), Longitubus (three species), Orcheosanthus (eight species), and Temnoceras (one species). Clade III included 16 species, which have been conventionally placed in section Agnata (four species), Crassifolia (four species), Heterophyllum (two species), Microphyllum (three species) and Orcheosanthus (three species). Clade II is widely distributed in the Sierra Madre Occidental, the Sierra Madre del Sur to the southern part of the Sierra Madre Oriental regions and extends down south to Honduras, while the species in clade III were mostly confined to the northern part of the Sierra Madre Oriental regions. In general, the ITS results were largely consistent with biogeographic patterns, but showed disagreements with the current morphological classification.
