Crassula ovata leaves appearing window-like

An unusual leaf-shape of Crassula ovata occurs in the form previously known as C. portulacea var. cristata and commonly called Shrek's ears. The blades of some of the leaves are not flat, but long and narrow, between cylindrical and cone-shaped. There is a distinctly curved, sometimes about circular but often skewed ridge at the leaf-tip, the wider end of the cone. The surface within the slightly red ring at the tip resembles the translucent window that lets sunlight into the leaves of some southern African succulents, including some Lithops species.

In these plants the sunlight is conveyed internally from the translucent window downwards via some transparent crystals of oxalic acid, positioned along the inside of the cylinder or cone. Near the bottom, on the inside surface of the cylinder, the sunlight reaches grains of chlorophyll found along the inner leaf walls of the leaf. Photosynthesis occurs here, facilitated by sunlight entering the succulent leaves (Smith, et al, 1997; www.asknature.org).