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   Sex Life Of Figs: Coevolution Of A Tree & Minute Wasp (Part 2)     Part 1       Part 2       Cystoliths  
© W.P. Armstrong Updated 7 October 2024

Cystoliths: Microscopic Calcium Deposits in Fig Leaves

Introduction To Mineral Deposits In Figs

As I have stated many times in my online and published articles that figs (genus Ficus) are truly the most remarkable and fascinating arborescent flowering plants. With an estimated 900+ monoecious & dioecious fig species on our planet, each with one or more unique, symbiotic, pollinator wasps, the fig & fig wasp scenario is the most complex interaction between a plant and an insect on Earth! I have been studying figs for over 40 years, starting with my former student Steve Disparti and a brilliant botany professor at UC Riverside (William B. Storey) and writings of the legendary UC botanist Dr. Ira J. Condit. I have taken thousands of images of wild tropical fig species on Palomar College field trips and cultivated figs in parks and gardens. In fact, on a Palomar field trip to the Florida Keys a passerby asked why I was photographing epiphytic strangler figs on walls and buildings. We told him that we were "Fig Busters" saving the Florida Keys from strangler figs. One of the students even made license plate frames for our group. My thousands of fig images and observations have been uploaded to Wayne's Word pages and some have appeared in books about figs.

  License Plate Frame On My Former Jeep Cherokee!  

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.

Close-up view of one cystolith in above adaxial leaf images of Ficus microcarpa. I believe it also shows central cellulose or siliceous stalk upon which calcium carbonate cystolith is formed. The stalk also supports cystolith within epidermal cell called a lithocyst. With minimal depth of field this is a difficult shot to get with limited viewing clarity through Sony W-300 pocket camera attached to eye piece of Olympus compound microscope. Using 10x objective (100x magnification) and extensive cropping, the total magnification oviously exceeds 200x.

Note: The following reference has descriptions and SEM images of Ficus cystoliths with central stalk that compare with my closeup image.

ABHIPSA MOHAPATRA & M. K. JANARTHANAM. 2020. "Cystolith Micromorphology in Selected Taxa of Ficus L. (Moraceae) in India and its Taxonomic Implications." Phytotaxa 436 (2): 167–181. https://www.mapress.com/j/pt/

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:

  Peer Review & Correspondence  


The following illustration is from my textbook by Katherine Esau from Plant Anatomy course at CA State Univ., LA during previous millennium (2nd millennium, 20 Century AD). It shows mature, stalked calcium carbonate cystolith & developing cystolith (from silica stalk) in upper epidermis of Ficus elastica. The mature cystolith is within enlarged cell (crystalliferous idioblast) or lithocyst.

Some of the following images show numerous cystoliths in leaves of Ficus microcarpa, a common fig used in bonsai & often confused with F. retusa. They occur in the upper & lower epidermis, and according to following reference, they increase the photosynthetic efficiency of F. microcarpa. In F. carica they only occur in lower epidermis and apparently do not increase photosynthetic efficiency. One hypothesis for cystoliths is they may fascilitate the tranfser of light to receptive photosynthetic chloroplast-bearing leaf cells. This is especially true on the shaded lower leaf surfaces by directing (distributing) light through upper layers of leaf tissue.

"Mineral Deposits in Ficus Leaves: Morphologies and Locations in Relation to Function"

Maria Pierantoni, Ron Tenne, Batel Rephael, Vlad Brumfeld, Adam van Casteren,
Kornelius Kupczik, Dan Oron, Lia Addadi, and Steve Weiner

Plant Physiology, February 2018, Vol. 176 (2), pp. 1751–1763

Disclaimer: I have been referring to the numerous mineral deposits in my Ficus leaf images as cystoliths; however, several scholarly articles about fig leaf anatomy mention other microscopic structures. These include stalked salt-glandular trichomes, non-glandular trichomes, mineralized spikes, silicified trichomes and cellulose stalk that generates & supports calcium carbonate cystolith. Some of these may appear in my images.


Some references list these calcium deposits within enlarged epidermal cells of some Ficus leaves as crystalliferous idioblasts. Left image shows crystalliferous idioblast in basswood stem (Tilia americana).


Leaf Anatomy of Ficus rubiginosa Very Different From F. microcarpa

The leaves of rustyleaf fig (Ficus rubiginosa) are brown on the underside due to tangled mass of branched, brown hairs (trichomes). Microscopic examination reveals they are very different from the leaves of F. microcarpa. There also appear to be lithocysts partially concealed by the brown hairs. Both fig species from southeast Asia and Australia are commonly cultivated in San Diego County. In fact I have documented and photographed the native pollinator wasps for F. rubiginosa (Pleistodontes imperialis) and F. microcarpa (Eupristina verticillata) on the campus of Palomar College. See my following fig pages:

  Sex Life Of Figs & Fig Wasps   
Banana Fig & Other Species

The brown hairs (trichomes) on underside of rustyleaf fig leaves produce unique rust color of leaf surface; however, the color is variable depending on density of hairs. This species is easily distinguished from leaves of F. microcarpa.

Although underside (abaxial surface) of leaf appears glabrous to naked eye, the veins are covered with minute hairs (trichomes). The general term for plant part covered with trichomes is pubescent. The microscopic white dots are calcareous deposits caled cystolths within enlarged epidermal cells called lithocysts.


Spherical cystoliths on lower (abaxial) surface of Ficus carica leaf. They do not occur on upper (adaxial) surface. Illustration (left) modified from University of South Florida clip art.

Disclaimer: I have been referring to the numerous mineral deposits in my Ficus leaf images as cystoliths; however, several scholarly articles about fig leaf anatomy mention other microscopic structures. These include stalked salt-glandular trichomes, non-glandular trichomes, mineralized spikes, silicified trichomes and cellulose stalk that generates & supports calcium carbonate cystolith. Some of these may appear in my images.

Spherical Cystoliths On Underside of Ficus carica Leaf


In order to find a more transparent fig leaf for microscope backlighting I decided to try my indoor Ficus carica. Its leaves were thinner because it was never grown outdoors in sunlight. It was grown from seed from my 'Vista Caprifig' mammoni syconium. This fig is especially noteworthy because it was grown from a male tree, and typically female trees produce seeds. Pollinated mammoni syconia mostly produce fig wasps when female fig wasp has laid eggs (oviposited) in ovaries of female flowers within syconium. If she fails to oviposit the ovary may produce a viable, seed-bearing endocarp. This is explained in more detail at following link.

  Seed-Bearing Mammoni Endocarps  

Cystoliths On Abaxial Surface (Underside) of Indoor Caprifig Leaf


The Mulberry Family Includes The Fig (Ficus) & Mulberry (Morus)

Figs (Ficus) and mulberries (Morus) belong to the mulberry family (Moraceae) and have some similar characteristics, including cystoliths in their leaves. Some members of the nettle family (Urticaceae) also have cystoliths in their leaves. In fact, in the order Rosales phylogenetic cladogram based on DNA, the 2 families are sister clades and branch from a common node (see following cladogram).

Mulberry leaf too thick for adequate backlit image with compound microscope. Epidermal layer ideally needs to be peeled to show transparent detail of cells; however, it is sufficient to verify multiple cystoliths on lower (abaxial) surface of leaf. Magnification 100x.