Pereskia

Phylogenetics: Pereskia has been repeatedly found to be paraphyletic by Nyffeler (2002), Edwards & al. (2005), and Butterworth & Edwards (2008). The genus forms a grade at the base of the Cactaceae, with a northern clade including Mesoamerican and Caribbean Pereskias as the first branching group followed by a southern clade, with mainly the Andean Pereskias, that also include the nomenclatural type of Pereskia (Butterworth & Wallace 2005; Edwards & al. 2005). No nomenclatural changes to reflect the paraphyly of Pereskia have been proposed by Edwards & al. (2005), who preferred their results to be tested with additional genes before suggesting a new classification for Pereskia. Also, no generic name was readily available for the northern Pereskia clade – the type of earlier-proposed segregate Rhodocactus was in the southern clade together with the type of Pereskia itself. An evolutionary instead of phylogenetic classification for Pereskia was favoured because both Pereskia clades have characters that are interpreted as ancestral within Cactaceae, such as a woody stem, the presence of true leaves, a flower morphology that differs from the rest of the Cactaceae and C₃ photosynthesis. Only recently, the northern Pereskias were segregated as Leuenbergeria (Lodé 2013), yet this segregation also received criticism because the two clades are hard to distinguish morphologically (http://www.mobot.org/MOBOT/research/Edge/apr13/apr13lit.shtml; Hunt 2013). Seeking a compromise between molecular phylogenetic hypotheses and nomenclatural stability, Rowley (2013) suggested a subgenus Leuenbergera (note the different spelling) for the northern Pereskia clade.A