Edwards E. J., Donoghue M. J., Pereskia and the Origin of the Cactus Life‐Form, The American Naturalist, 2006, 167(6):777-793, doi: 10.1086/504605
Field measurements of seven leafy cacti were compared with phylogeny and site climate. The account helps explain how water conservation may have preceded strongly succulent stems. Pereskia in this paper also includes species now assigned to Leuenbergeria.