Phylogenetic analysis of Peniocereus (Cactaceae, Echinocereeae) based on five chloroplast DNA markers

The genus Peniocereus contains distinctive cacti with slender stems and thickened roots. The phylogenetic relationship of Peniocereus to other members of the subtribe Pachycereinae is unresolved, and a sister group for the genus has not been suggested in previous molecular phylogenies. Therefore, this study aims to corroborate the monophyly of Peniocereus, to determine the relationships within the genus, to clarify their relationship with Nyctocereus, and to reconstruct the ancestral states for eight morphological characters and the areas of distribution. Five chloroplast markers (rpl16, petL-psbE, psbA-trnH, trnL-trnF, and rpl32-trnL) and a broad outgroup represented by all genera of the subtribes Pachycereinae and Echinocereinae were used in phylogenetic analyses. The results strongly supported the monophyly of Peniocereus, which comprises P. greggii, P. johnstonii, P. lazaro-cardenasii, P. marianus, P. striatus, P. viperinus, and P. zopilotensis. The genus was sister to the Pachycereus group, which comprises Carnegiea, Lophocereus, Marshallocereus, Nyctocereus, and Pachycereus (including Backebergia and Pterocereus). The scandent branches, slender stems, and papillose epidermis are ancestral characters to Peniocereus. A complex region including the Pacific Lowlands, the Balsas Basin, and the Sonoran Desert was inferred as the ancestral area for the genus. This work provides the most comprehensive phylogeny of the subtribe Pachycereinae.