Many recent authors apply a broad definition of the family Hydrophilidae. This concept of a Hydrophilidae sensu lato also includes the genera Epimetopus, Eumetopus, Eupotemus, Helophorus, Georissus, Hydrochus and Spercheus. Short and Fikacek (2013) have performed a large-scale molecular phylogeny analysis incorporating data from most hydrophiloid genera. They advocate a more narrow concept of the Hydrophilidae, that does not include the above genera. I follow here the analysis by Short and Fikacek (2013) and use the narrow concept of Hydrophilidae that relegates the above genera to separate families Epimetopidae, Helophoridae, Georissidae, Hydrochidae and Spercheidae. However, I also note three problematic issues with this concept:
(1) the genus Epimetopus (Eumetopus and Eupotemus have not been included in the study by Short and Fikacek (2013)) is clearly more closely related to the Hydrophilidae sensu stricto than are the other excluded genera. In the analysis they form the sister clade of the Hydrophilidae s.str. and therefore they might be better classified as a subfamily Epimetopinae within the Hydrophilidae.
(2) While Hydrochus, Georissus and Helophorus clearly form a separate clade (and therefore their exclusion from Hydrophilidae seems justified), the placement of the genus Spercheus is unresolved in the phylogeny by Short and Fikacek (2013). Thus, more work is neccessary before its status as a separate family can be justified.
(3) The genera Hydrochus, Georissus and Helophorus form a well-supported monophyletic clade in the analysis by Short and Fikacek (2013). Thus, these genera could be merged into a single family to better reflect this fact.
Thus, further changes in the taxonomy of the hydrophiloid groups might be warranted in the future, when more information about the basal branches in the phylogenetic tree will become available.