Mauseth J. D., Landrum J. V., Relictual vegetative anatomical characters in Cactaceae: the genus Pereskia, Journal of Plant Research, 1997, 110(1):55-64, doi: 10.1007/bf02506843
The vegetative anatomy comparison includes Pereskia in its historical broad sense. It compares leaves, primary cortex and wood with more strongly succulent cacti.