[4] The term pruinosity is also applied to "blooms" on plants—for example, on the skin of grapes[6]—and to powderings on the cap and stem of mushrooms, which can be important for identification.
Pruina in lichens frequently consists of calcium oxalate crystals deposited on the surface of the thallus or reproductive structures.
In the family Teloschistaceae, these crystalline deposits serve multiple ecological functions, including protection against excessive sunlight.
The abundance of pruina can vary significantly depending on environmental conditions, with some species showing increased crystal formation when exposed to higher levels of solar radiation.
However, because pruina formation is heavily influenced by environmental factors, it is generally considered less reliable for taxonomic purposes than internal crystalline deposits.