Interfamilial relationships of Cactaceae within the dicot order, Caryophyllales

The position of the cactus family, Cactaceae, within the order Caryophyllales was examined by outgroup analysis of chloroplast rbcL gene sequence data. Comparative data came from 28 outgroup species in 15 families and six ingroup species. Phylogenetic Analysis with PAUP 3.1 produced twelve equally parsimonious trees; these were used to generate a strict consensus tree. MacClade 3.06 was used to refine the polytomies in the consensus tree. Analysis indicates that the Cactaceae is a monophyletic clade; moreover, these results support the work of other analyses that the sister family to Cactaceae is the Portulacaceae. Other relationships within the order are not completely consistent with previous studies. For example Molluginaceae and Caryophyllaceae occupy a central position in the cladogram; Achatocarpaceae aligns with the Amaranthaceae and Chenopodiaceae; and Basellaceae is presented as the basal family within the order. Lastly, the Jamaican cactus Opuntia spinosissima was derived from a common ancestor with the Florida Keys endemic, Opuntia corallicola.