Bostrichiformia Cucujiformia Elateriformia Scarabaeiformia Staphyliniformia Polyphaga is the largest and most diverse suborder of beetles.

The five main infraorders are: Phylogenetic studies have also suggested that Scirtoidea (Scirtidae, Decliniidae), Clamboidea (Clambidae, Derodontidae, Eucinetidae), Rhinorhipus and Nosodendridae are independent lineages of Polyphaga that lie outside these groups.

[2] The internal classification of Polyphaga involves several superfamilies or series, whose constituents are relatively stable, although some smaller families (whose rank even is disputed) are allocated to different clades by different authors.

The infraorder Cucujiformia includes the vast majority of phytophagous (plant-eating) beetles, united by cryptonephric Malpighian tubules of the normal type, a cone ommatidium with open rhabdom, and lack of functional spiracles on the eighth abdominal segment.

Evidently adoption of a phytophagous lifestyle correlates with taxon diversity in beetles, with Cucujiformia, especially weevils (Curculionoidea), forming a major radiation.