Vascular Plants of the Gila Wilderness

*Farina is an amorphous white or yellow substance covering the undersurface (abaxial surface) of this and some other types of ferns. From the American Fern Journal, vol. 68 no.1 by Eckhard Wollenweber:
"The farinose coating of these plants is not excreted by the entire epidermis, like a true wax coating, but is formed exclusively by the globose terminal cell of small hairs which have a short, unicellular stalk. The wax is exuded on the whole surface of the terminal cells in the shape of rod- or needle-like crystals... It is striking that the components of fern farina are almost exclusively methyl derivatives of flavonoids and so are rather non-polar compounds..."
Flavonoids are water soluble plant pigments, complex aromatic compounds with 2 phenyl rings and other constituents. It has variously been suggested that the presence of these compounds on ferns makes the surface more reflective and therefore less susceptible to intense sunlight or that it makes the plant less palatable to potential browsers.