In leptosporangiate ferns, the annulus located on the outer rim of the sporangium and serves in spore dispersal. It consists typically of a ring or belt of dead water-filled cells with differentially thickened cell walls that stretches about two-thirds around each sporangium in leptosporangiate ferns.

What is the function of the annulus?

The annulus is a sturdy tire-like structure that encases a gel-like center, the nucleus pulposus. The annulus enhances the spine's rotational stability and helps to resist compressive stress. The annulus is a layered structure consisting of water and sturdy elastic collagen fibers.

What is annulus?

1 : ring. 2 : a part, structure, or marking resembling a ring: such as. a : a line of cells around a fern sporangium that ruptures the sporangium by contracting. b : a growth ring (as on the scale of a fish) that is used in estimating age.