or 2 genera, about 90 species, worldwide.
circumscription of the Potamogetonaceae has undergone revision during the past
few decades. The family, as traditionally circumscribed, includes genera here
treated in the Najadaceae, Ruppiaceae, and Zannichelliaceae. Some
authors continue to place various of these groups, particularly the genus Ruppia,
into the Potamogetonaceae, and the precise intergeneric relationships still
require further study.