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Pruinescence is found in many species of Odonata, particularly damselfly of the families Lestidae and Coenagrionidae, where it occurs on the wings and body. Among true dragonfly it is most common on male Libellulidae (skimmers).
In the common whitetail and blue dasher dragonflies ( Plathemis lydia and Pachydiplax longipennis), males display the pruinescence on the back of the abdomen to other males as a territorial threat. Other Odonata may use pruinescence to recognize members of their own species or to cool their bodies by reflecting radiation away.
Pruina in 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. Studies have also suggested that pruinose deposits may help lichens neutralize the effects of certain , such as sulfur dioxide, with evidence indicating that the amount of surface pruina may correlate with local pollution levels.
While pruina is often a response to environmental conditions, its presence and distribution can sometimes serve as a taxonomic feature in lichen identification. However, because pruina formation is heavily influenced by environmental factors, it is generally considered less reliable for taxonomic purposes than internal crystalline deposits. The composition of pruina can vary, with calcium oxalate occurring in two distinct mineral forms: weddellite (CaC2O4·(2+x)H2O), which is typically found in dry environments and may serve as a water source for the lichen, and whewellite (CaC2O4·H2O), which is more commonly found in moist habitats.
An epinecral layer is "a layer of horny dead fungal hyphae with indistinct lumina in or near the cortex above the algal layer".Pruina as a Taxonomic Character of the Lichen Genus Dermatocarpon, Starri Heidmarsson, The Bryologist Vol. 99, No. 3 (Autumn, 1996), pp. 315-320, [2]
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