Anneau (champignon)

An annulus is the ring-like or collar-like structure sometimes found on the stipe of some species of mushrooms. The annulus represents the remnants of the partial veil, after it has ruptured to expose the gills or other spore-producing surface. It can also be called a ring which is what the Latin word annulus directly translates as. The modern usage of the Latin word originates from the early days of botany and mycology when species descriptions were only written in Latin. Outside of the formal setting of scientific publications which still have a Latin requirement, it will often just be referred to as a ring or stem ring in field guides and on identification websites. The way in which the structure and appearance of rings is described can vary with author and the description may only note the existence of a ring without providing specific information in cases where the ring lacks any notable features that would be useful to distinguish between similar species. Ring shapes and structures can also vary between specimens of the same species and change with the age of the mushroom so multiple descriptions are sometimes used. Even in species with distinctly identifiable rings they may not always be present or perfectly match descriptions so it can be beneficial to have multiple specimens to compare at different states of maturity. Some rings may be persistent and remain through the life of the mushroom or they may disappear with age. Such rings have a variety of synonymous terms associated with them such as fleeting, ephemeral, evanescent, transient, fugacious or impermanent. These rings may peel away from the stem, fall apart or simply fade into the stem surface as it matures. Rings may also be described as fragile, meaning easily torn or damaged and whilst some fragile rings could be considered permanent if undisturbed they are often likely to vanish due to their fragility. Some rings may be fixed in place and firmly attached to the stem whilst others may be movable or mobile with the ability to slide up and down the stem either by hand or just falling down naturally with age.