Pruinescence

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Within biology, pruinescence is a form of epicuticular wax—a protective layer covering fruit, leaves, and other parts of a plant's morphology.

 

also known as pruinose and pruina

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Pruinescence is a whitish wax coating or fine white powder covering several kinds of fruit, leaves, and other parts of a plant's morphology. It's that fine powdery coating you find on grapes, plums, and on the leaves of several succulents. It's a plant's way of protecting itself: from loss of moisture, and excessive surface wetting, to bacterial and fungal invasion, as well as deterring overzealous insects—their claws incapable of finding decent traction.

Almost all plants have some form of epicuticular wax to protect them—often translucent in nature—but when it's white in colour, we have the rather poetic option of naming it pruinescence. The wax deters water from penetrating the cuticle, by doing so a self-cleaning action is created. Water can't go in, so instead it falls or rolls away, and takes with it any dirt clinging to the surface. The wax has another function, depending from plant to plant, it holds varying degrees of UV (ultraviolet) reflective qualities. This quality protects it from excess sun damage, but it also adds an extra layer of narrative. You see, much of nature is hidden from us, our senses only allow what they allow and what our conscious mind decides to hold importance to. What might look ordinary to us is extraordinary under the right sense.

To us it appears as varying shades of white, but to those creatures capable of observing UV light another narrative unfolds—one of invitation or warning. It's quite tempting as humans to think our view of the world is the only that matters, that the whole of it was built to serve us, but nothing could be further from the truth. It's humbling to realise just how little we are capable of registering, the wide range of communication we stand outside of. But, it's also fascinating, because our technology, as it grows and specialises, compensates for what we cannot register through our own physical means.

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Outside of Botany

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The term isn't unique to botany, it's used in entomology—the study of insects—as well. Pruinescence is a system of communication: to recognise one's own species, and to warn and deter others. When applied to insects, pruinescence still implies a wax coating, but it's colours can vary from white to pale blue, and a few others.

At least to us, it appears as those colours, to insects, capable of seeing UV light they appear quite different. For us, what might appear as different colours, to them might mean different strengths of UV reflectivity.

Those most associated with pruinescense belong to the Odonata order, which contains dragonflies and damselflies. As with plants, the amount of wax created differs between species, but it can also differ between the female and the male of the species, known as sexual dimorphism. With males showing a greater production of pruinescence (Gorb, 1995).

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Etymology

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to become like frost | to glisten like frost

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pruina

frost | freeze

From Latin

-escence

to become | a state of being | a process

Middle French, derived from the Latin -escentia. A suffix attached to words to denote a process or state of being.

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As a Specific Epithet

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pruinatus | pruinata | pruinatum | pruinosus | pruinosa | pruinosum

As a specific epithet the name is used within botany, mycology, and zoology. It's given to those with a whitish or frosted coating or appearance. It's not always clear, on first glance, which physical characteristic the name refers to.

examples

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Xerocomellus pruinatus | a mushroom belonging to the Boletaceae family, its members are known for their thick stems and caps. Their appearance, as well as their relative safety, make them ideal for novice mushroom hunters. Xerocomellus pruinatus is known under its common name of matte bolete.

Stenocereus pruinosus | a cactus with a green colouring and a light white coating. All cacti belong to the Cactaceae family, which in turn is divided up into a few subfamilies and several tribes.

Physalis pruinosa | a species of physalis, commonly known as strawberry groundcherry—which if you give it too much thought becomes a stranger name which each passing second. They belong to the same family, Solanaceae or nightshade, as tomatoes (Solanum lycopersicum), potatoes (Solanum tuberosum), tobacco (Nicotiana tabacum), and goji berries (Lycium barbarum). It's papery husk has a light beige colour, and the berries a pale yellow.

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As an adjective

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pruinose

Pruinose, to describe something that appears whitish, frosted, or covered with fine white powder.



Notes

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Though, it's a rather nice word, pruinescence doesn't seem to be in great use any longer, at least not within botany. Pruinescence hints at a frost like appearance. But, true white doesn't exist in nature, it can't, colour doesn't exist in a vacuum, it is constantly influenced by all the others that surround it. So what is white or pruinose in nature, might to another be glaucous, a pale greyish-blue or green epicuticular wax.

Colours always influence one another, and wether you'd like to call something pruinose or glaucous, you have to keep in mind that epicuticular wax is never so thick and opaque as to completely cover the colour of the cuticle underneath it. So, if the skin of the fruit is a purple blue, won't the colour of the wax lean more towards glaucous, or might it by its very contrast lean more towards pruinescence? Both words do seem to have a clearer definition within zoology and entomology.


More on Morphology

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