Unique type of angiosperm pollen from the family annonaceae

The primitive antgiosperm family Annonaceae possesses a remarkable type of pollen that appears unique in its size (diameter up to 350 micrometers), lack of exine over nearly 50 percent of the grain surface at maturity, and proximalipolar aperture. This unique pollent is further distinguished by being in polyads which are compartmentalized individually within septate stamens.