Systematic study and niche differentiation of the genus <em>Aporocactus</em> (Hylocereeae, Cactoideae, Cactaceae)

Background: Aporocactus is an epiphytic or saxicolous genus that is endemic to Mexico and has a distribution restricted to cloud forests and pine-oak forests. As with many cacti, Aporocactus presents taxonomic conflicts, especially regarding species delimitation, since five species in this genus have been described and accepted by some authors, while others accept only two species.Questions: How many species comprise Aporocactus? What are their relationships? Do these species show differences in their climatic preferences?Studied species: The five putative species in Aporocactus were investigated.Study site and dates: This study was conducted in 2015 and 2016. The collection sites were in Hidalgo, Puebla, Querétaro, Veracruz, and Oaxaca states, Mexico.Methods: In this study, phylogenetic analyses were performed using chloroplast DNA markers from different Aporocactus populations and related genera, and ecological niche modeling techniques were also employed.Results: The phylogenetic analyses indicated that Aporocactus is composed of only two species: A. flagelliformis and A. martianus. Additionally, the phylogenetic analyses corroborated that Aporocactus is an early diverging group related to Weberocereus and Selenicereus. Finally, niche modeling and niche identity testing indicated that the niches of the two species of Aporocactus are significantly differentiated and niches are more different than would be expected by chance.Conclusions: Despite being a genus with only two species, Aporocactus represents a useful model for investigating such topics as the ecology of pollination, genetic populations, and flower development to characterize the evolution of these specialized cacti.