Ozerova L. V., Timonin A. C., Cacti defeat physics: columnar chlorenchyma in tubercles of three species of Mammillaria Haw. (Cactaceae), Wulfenia, 2020, 27:10-20
A comparison of tubercle anatomy in three Mammillaria species from greenhouse material, using transverse and longitudinal sections and light and scanning microscopy. The paper describes vascular bundles, the absence of a distinct hydrenchyma and the columnar arrangement of outer chlorenchyma cells. The discussion links this arrangement to gas diffusion, vacuole volume and CAM photosynthesis, and presents a hypothesis of its importance in the evolution of the succulent stem.