What is "orbicule"

Orbicules (syn. Ubisch bodies, con-peito grains) are small acellular structures of sporopollenin (known size range from < 1 µm to 15 µm, but usually sub-micrometre) that might occur on the inner tangential and radial walls of tapetal cells. Their function is unclear at this moment. Current consensus is that they are just a by-product of pollen wall sporopollenin synthesis.