An
annulus is the ring like structure sometimes found on the
stipe of some species of
mushrooms. The annulus represents the remaining part of the
partial veil, after it has ruptured to expose the
gills or other spore-producing surface. An annulus may be thick and membranous, or it may be cobweb-like. An annulus may be persistent and be a noticeable feature of a mature mushroom, or it may disappear soon after the emergence of the mushroom, perhaps leaving a few remnants on the stipe as an "annular zone".