Cystoliths are mineral deposits within enlarged epidermal cells called lithocysts. They were discovered in a species of fig almost 200 years ago. Some references refer to these cells as crystalliferous idioblasts containing crystals of calcium carbonate, calcium oxalate or silica. They are apparently variable in size, shape and crystalline composition & structure. In fact, they may be useful in identifying species in the enormous fig complex. They can range in size from 70 to 300 micrometers (µ). The largest are about the size of ordinary grains of table salt (0.3 mm = 300 µ) and are visible with naked eye. According to Katherine Esau (Plant Anatomy, 1965), they are common in leaves of Ficus species (mulberry family--Moraceae). In fact, they also occur in mulberry leaves (genus Morus). Most of the scholarly references I have consulted only show highly magnified (SEM) illustrations. I must confess that I haven't seen many images at microscope magnifications like the following.

Some online references describe white spots on Ficus elastica leaves as hydathodes (guttation pores) where excess water droplets are released, while others call them lithocysts. Actually, these are 2 different structures. Steve Disparti has identified and photographed hydathodes on an unidentified, volunteer fig in the following 2 images. The hydathodes are fewer in number, larger in size, and generally appear closer to outer areas of leaf (closer to margins) compared with numerous, microscopic cystoliths throughout leaf epidermal layers. Hydathodes in fig leaves typically occur at the confluence of small veins (veinlets) that merge into hydathode (exit pore) in upper or lower epidermis.

Hydathodes are often visible oval spots on leaves, and are sometimes incorrectly interpreted as a disease to one's prized cultivated fig. In the following images of a F. microcarpa upper (adaxial) leaf surface, I only detected hydathodes when examined with B & L dissecting microscope at 15x magnification.

I am reasonably certain the following images are microscopic cystoliths (calcium deposition) on leaves of Ficus microcarpa, F. rubiginosa and F. carica. The leaves were not microsectioned to make them more transparent; however, my images are good enough to recognize these microscopic calcareous crystals. Ideally, they need an epidermal peel or clearing to show more cellular detail with backlighting. Since my academic biology website (Wayne's Word) is now hosted by Network Solutions, it may no longer be peer-reviewed by hundreds of authorities when it resided on the Palomar College server. I am definitely in the market for an academic host for Wayne's Word that allows a static html website on a secure server, preferably a college, museum or botanical garden. See my peer review pages: