Pilularia globulifera, or pillwort,<ref name=BSBI07>Template:Cite web</ref> is an unusual species of fern native to western Europe,<ref>Template:IUCN</ref> where it grows at edges of lakes, ponds, ditches and marshes, on wet clay or clay-sand soil, sometimes in water up to Template:Convert deep.
Pillwort grows on silt and mud at the margins of lakes, ponds and other watercourses that are submerged for at least part of the year.<ref name=Stace>Template:Cite book</ref>Template:Rp Some of the plants growing in association with this species in the UK include water celery (Apium inundatum), marsh pennywort (Hydrocotyle vulgaris) and lesser spearwort (Ranunculus flammula).
This is a rare species, declining as its wetland habitats are reduced by eutrophication and drainage, but is regarded as of least concern by the IUCN Red List. It is listed on Schedule 8 of the Wildlife (Northern Ireland) Order 1985, but it has not been seen there since 1970 and may now be extinct in the province. It is protected under the Wildlife and Countryside Act 1981 in the rest of the UK, where it is now classified as Vulnerable.Template:Citation needed
Pillwort can be grown in a "bog garden" or as a marginal aquatic in a garden pond.Template:Citation needed