Oakmoss (Evernia prunastri) is, strictly speaking, not a plant at all but a lichen — a symbiosis of fungus and algae — growing as grey-green, branching tufts on the bark of oaks and other deciduous trees across the temperate forests of Europe. Unlike flowering plants, the lichen draws part of its nutrients directly from the air, which makes it especially sensitive to air pollution and is why it is traditionally harvested from the tree by hand. Several hundred lichen species in the genus Evernia and related genera are known worldwide, yet only a handful possess the distinctive scent profile that suits them for perfumery.

Oakmoss ranks among the oldest and most significant materials in perfumery, already appearing in ancient Egyptian fragrance recipes. Since François Coty created his landmark scent "Chypre" in 1917, oakmoss has been the namesake heart of the entire chypre family of perfumes, and it appears in classic compositions such as "Mousse de Saxe." Traditionally, it was harvested chiefly from the oak forests of the former Yugoslavia and France. Because certain compounds in the raw extract can trigger skin allergies, its use in modern perfumery is now tightly restricted under the rules of the International Fragrance Association (IFRA). As a lichen, oakmoss is so sensitive to airborne pollutants that biologists still use it today as a natural bioindicator of a forest's air quality. Historically it also served as a source of natural dye for coloring wool and textiles. Because the raw extract's allergens now limit its use, perfumers increasingly turn to semi-synthetic substitutes that aim to recreate the characteristic earthy, mossy chypre accord, even if they rarely match its full depth.

Burned as incense, oakmoss releases a deep, earthy, mossy-woody scent with a damp, almost leathery note — reminiscent of a forest floor after rain. It has a strongly grounding effect, associated with connection to ancient forests and deep rootedness. In the traditional harvesting regions of the Balkans, hand-picking oakmoss still forms an important seasonal source of income for some families today. Together with bergamot and labdanum, oakmoss forms the classic triad on which the entire chypre fragrance family has been built ever since Coty's original creation.