Pruinescence , or pruinosity, is a "frosted" or dusty-looking coating on top of a surface. It may also be called a pruina (plural: ''pruinae''), from the Latin word for hoarfrost. The adjectival form is pruinose .

Entomology

In insects, a "bloom" caused by wax particles on top of an insect's

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

covers up the underlying coloration, giving a dusty or frosted appearance. The pruinescence is commonly white to pale blue in color but can be gray, pink, purple, or red; these colors may be produced by

Tyndall scattering The Tyndall effect is light scattering by particles in a colloid such as a very fine suspension (a sol). Also known as Tyndall scattering, it is similar to Rayleigh scattering, in that the intensity of the scattered light is inversely proport ...

of light. When pale in color, pruinescence often strongly reflects

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

. Pruinescence is found in many species of

Odonata Odonata is an order of predatory flying insects that includes the dragonflies and damselflies (as well as the '' Epiophlebia'' damsel-dragonflies). The two major groups are distinguished with dragonflies (Anisoptera) usually being bulkier with ...

, particularly

damselflies Damselflies are flying insects of the suborder Zygoptera in the order Odonata. They are similar to dragonflies (which constitute the other odonatan suborder, Epiprocta) but are usually smaller and have slimmer bodies. Most species fold the win ...

of the families

Lestidae The Lestidae are a rather small family of cosmopolitan, large-sized, slender Damselfly, damselflies, known commonly as the spreadwings or spread-winged damselflies. Characteristics While most Zygoptera, damselflies rest with their wings folded ...

and

Coenagrionidae Coenagrionidae is a family of damselflies, also known as pond damselflies, in the order Odonata and the suborder Zygoptera. The Zygoptera are the damselflies, which although less known than the dragonflies, are no less common. More than 1,300 spec ...

, where it occurs on the wings and body. Among true

dragonflies A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threate ...

it is most common on male

Libellulidae The chasers, darters, skimmers, and perchers and their relatives form the Libellulidae, the largest family of dragonflies. It is sometimes considered to contain the Corduliidae as the subfamily Corduliinae and the Macromiidae as the subfamily M ...

(skimmers). In the common whitetail and

blue dasher The blue dasher (''Pachydiplax longipennis'') is an insect of the skimmer family. It is the only species in the genus ''Pachydiplax''. It is widely distributed throughout North America and into the Bahamas. Although the species name ''longipennis ...

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.

Plants, fungi, and lichens

The term ''pruinosity'' is also applied to "blooms" on plants—for example, on the skin of

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began approximately 8,0 ...

s''‘Sangiovese’ and ‘Garganega’ are two key varieties of the Italian grapevine assortment evolution''
, M. Crespan, A. Calò, S. Giannetto, A. Sparacio, P. Storchi and A. Costacurta, Vitis 47 (2), 97–104 (2008); p. 98-99 discusses different

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

s of ''

Vitis vinifera ''Vitis vinifera'', the common grape vine, is a species of flowering plant, native to the Mediterranean Basin, Mediterranean region, Central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern ...

'' '

Catarratto Catarratto is a white Italian wine grape planted primarily in Sicily where it is the most widely planted grape. Catarratto can make full bodied wines with lemon notes.J. Robinson: ''Jancis Robinson's Wine Course'' Third Edition, p. 101. Abbevill ...

' showing varying pruinosity—and to powderings on the cap and stem of

mushroom A mushroom or toadstool is the fleshy, spore-bearing Sporocarp (fungi), fruiting body of a fungus, typically produced above ground on soil or another food source. ''Toadstool'' generally refers to a poisonous mushroom. The standard for the n ...

s, which can be important for identification. Pruina in

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

s frequently consists of

calcium oxalate Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula or . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydr ...

crystals deposited on the surface of the

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

or reproductive structures. In the family

Teloschistaceae The Teloschistaceae are a large family (biology), family of mostly lichen-forming fungi belonging to the class (taxonomy), class Lecanoromycetes in the division (botany), division Ascomycota. The family has a cosmopolitan distribution, althoug ...

, 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 Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible light perceptible to the human eye as well as invisible infrared (typically p ...

. Studies have also suggested that pruinose deposits may help lichens neutralize the effects of certain

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...

s, such as

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

, 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 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

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 A lichen ( , ) is a hybrid colony of algae or cyanobacteria living symbiotically among filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualistic relationship.

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

/ref>

References

{{reflist Insect morphology Plant morphology