Pruinus

Pruinus is a Latin term used in biology to describe a frosted or powdery surface. It is used in botanical descriptions to denote coatings on leaves, fruits, buds, or seeds, and the noun pruina denotes the coating itself. In English, the related adjective pruinose describes surfaces bearing pruina.

Pruina is produced by epidermal cells or surface secretions that form microscopic crystals or waxes. The resulting layer is a powdery, whitish, bluish, or translucent film that can cover entire surfaces or appear in patches. The degree of coverage and color can vary with species, developmental stage, and environmental conditions.

In plants, pruina commonly appears on young leaves, fruit skins, or seeds. A familiar example is the pale bloom often visible on grape berries, sometimes described as a powdery bloom. The coating also occurs on various stone fruits and on other fruit surfaces. In field and herbarium descriptions, a pruinose surface can be a useful taxonomic character that complements other traits for identification.

Possible functional roles of pruina include reducing water loss, reflecting excess light and ultraviolet radiation, and protecting tissues from abrasion or pathogens. It can also influence the apparent color of plant surfaces, which may affect interactions with pollinators, herbivores, or other organisms.

Overall, pruinus serves as a descriptive term in botany and related disciplines, helping to characterize surfaces and contribute to species descriptions in a neutral, evidence-based manner.