The phylogenetic significance of the stem morpho-anatomy in the Hylocereeae (Cactoideae, Cactaceae)

The Hylocereeae is a monophyletic group in which eight genera are recognized based on molecular data. However, relationships between the genera remain partially resolved. In this study, combined analyses of molecular and structural characters for Hylocereeae were carried out with the aims of finding structural synapomorphies that support the genera and to resolve relationships between them. We studied sixty-nine species of the eight genera of Hylocereeae, as well as six Echinocereeae species as outgroup using light microscopy and scanning electron microscopy. Thirty-six morpho-anatomical characters were incorporated into a matrix and analyzed in combination with sequences of four chloroplast DNA regions. Phylogenetic analyses using maximum parsimony, maximum likelihood, and Bayesian inference yielded a robust phylogenetic hypothesis and showed morphological synapomorphies. Four of the genera ( Acanthocereus , Aporocactus , Epiphyllum , and Kimnachia ) have at least one structural synapomorphy. Disocactus and Pseudorhipsalis can be recognized by a combination of characters, while Selenicereus and Weberocereus cannot be recognized by any structural vegetative character. There are structural synapomorphies that allow recognizing relationships between genera. The cortical and vascular characters are as important as the epidermal traits, a condition that had not been reported for another group within Cactaceae.