The genus Pilularia is a type of aquatic fern that is commonly known as pillwort. The genus has only two species, Pilularia globulifera and Pilularia novae-zelandiae, which are both found in different parts of the world. Pillwort is an interesting plant because of its unusual shape and the fact that it is one of the few freshwater ferns. It has been used in traditional medicine for a variety of ailments. Some synonyms for the genus Pilularia include pillwort fern, bladder fern, pea fern, and globe fern. These terms may be used interchangeably depending on the context and the region of the world in which the plant is found.