Penthoraceae Rydb. ex Britton is the accepted scientific name for this family of plants. It was named and described as such by Nathaniel Lord Britton in the Manual of the Flora of the Northern States and Canada in 1901 using a previous description by Per Axel Rydberg.
The genus Penthorum L. is the only accepted genus in the family and was named and described as such by Carl von Linnaeus in the first volume of the first edition of Species Plantarum in 1753.
There are only two species in the genus, Penthorum chinense and Penthorum sedoides. I seemed to have stumbled on the latter near the pond at the back of the farm which you can read about HERE.