Pereskia - Phylogeny and Evolution

Phylogeny and Evolution

A 2005 study suggested that the genus Pereskia was basal within the Cactaceae, but confirmed earlier suggestions that it was not monophyletic, i.e. did not include all the descendants of a common ancestor. The Bayesian consensus cladogram from this study is shown below.

The species studied divide into the two clades as shown below.

A more recent 2011 study using fewer genes also found that Pereskia was divided into these two clades.

The two clades of Pereskia differ in their geographical distribution: with one exception, Clade A is found around the Gulf of Mexico and the Caribbean Sea whereas Clade B occurs south of the Amazon Basin. Species of Pereskia within Clade A always lack two key features of the stem present in most of the remaining "caulocacti": like most non-cacti, their stems begin to form bark early in the plant's life and also lack stomata – structures which control the admission of air into a plant and hence control photosynthesis. By contrast, species of Pereskia Clade B typically delay forming bark and have stomata on their stems, thus giving the stem the potential to become a major organ for photosynthesis.

If Pereskia is divided into two genera, based on these two clades, then Rhodocactus is a possible name for Clade A.