Penthorum is a genus of plants in the order Saxifragales. They are erect herbaceous perennials about half a meter tall. The genus consists of two species, one from east Asia and one from eastern North America. It is variously classified in the family Saxifragaceae

Saxifragaceae

Saxifragaceae is a plant family with about 460 known species in 36 genera. In Europe there are 12 genera.The flowers are hermaphroditic and actinomorphic...

 or its own family Penthoraceae. Its closest relatives may be in Haloragaceae

Haloragaceae

Haloragaceae is a dicotyledon flowering plant family in the order Saxifragales, based on the phylogenetic APG III system. In the Cronquist system, it was included in the order Haloragales.- Distribution :...

.