The two clades of "Pereskia" sensu lato differ in their geographical distribution: with one exception, "Leuenbergeria" (Clade A) is found around the Gulf of Mexico and the Caribbean Sea whereas "Pereskia" s.s. (Clade B) occurs south of the Amazon Basin. Species of "Leuenbergeria" 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" s.s. typically delay forming bark and have stomata on their stems, thus giving the stem the potential to become a major organ for photosynthesis.