Fragilaria

{{Short description|Genus of single-celled organisms}}

{{Automatic taxobox

| image = Fragilaria crotonensis.jpeg

| image_caption = Fragilaria crotonensis

| taxon = Fragilaria

| authority = Lyngbye (1819)

| subdivision_ranks = Species

| subdivision = see text

}}

Fragilaria is a genus of freshwater and saltwater diatoms. It is usually a colonial diatom, forming filaments of cells mechanically joined by protrusions on the face and in the center of their valves. The individual diatoms appear swollen in their centers where they are joined to the colonial ribbon.{{cite book |last=Williams |first=David M. |url=https://www.springer.com/us/book/9789400713260 |title=The Diatom World |last2=Kociolek |first2=J. Patrick |date=2011-07-23 |publisher=Springer |isbn=978-94-007-1327-7 |editor-last=Seckbach |editor-first=Joseph |location=Dordrecht |page=61 |chapter=An Overview of Diatom Classification with Some Prospects for the Future |editor-last2=Kociolek |editor-first2=Patrick}} The genus grows as both plankton and benthic species, free living in colonies or as epiphytes. Some species are bloom forming diatoms in eutrophic lakes. The type species is Fragilaria pectinalis Lyngbye from designating a lectotype from Conferva pectinalis O.F.Müller.{{cite book|last1=Wehr|first1=John D.|last2=Sheath|first2=Robert G.|title=Freshwater Algae of North America: Ecology and Classification (Aquatic Ecology)|date=Jun 5, 2015|publisher=Elsevier|isbn=9780123858771}} The taxonomy of the genus is still uncertain.{{cite book|editor1-last=John|editor1-first=David M.|editor2-last=Whitton|editor2-first=Brian A.|editor3-last=Brook|editor3-first=Alan J.|title=The Freshwater Algal Flora of the British Isles : An Identification Guide to Freshwater and Terrestrial Algae|date=2011|publisher=Cambridge University Press|location=Cambridge|isbn=9780521193757|edition=2nd}}

Fragilaria has been the dominant genus of diatoms in Lake Mývatn in Iceland for at least 1200 years. The genus currently accounts for around 93% of all diatoms in the lake.