A parsimony analysis was undertaken to test subfamily and tribal group concepts of Cassidinae (ca. 2000 genera, ca. 6000 species). An integrated account of their biology was synthesized from the primary literature. A detailed morphological study of adults, using Hemisphaerota palmarum Boheman as a model, formed the basis for evaluating characters previously utilized and for defining novel characters. The data matrix comprised 210 characters (from adults and immature stages, ecology and behavior), 6 outgroups, and 98 ingroup exemplar species (representing 94 genera and 39 of the 43 recognized cassidine tribes). Results support the monophyly of Cassidinae and place it as sister to Galerucinae. The classical Hispinae s.str. is paraphyletic whereas the classical Cassidinae s.str. is monophyletic if some Imatidiine genera are included. Four tribes—Aproidini, Delocraniini, Hemisphaerotini, and Notosacanthini—are well supported by many autapomorphies. Multiple genera were sampled to test the monophyly of 14 cassidine tribes. Seven were recovered as monophyletic: Anisoderini, Cassidini, Dorynotini, Eugenysini, Hispini, Omocerini, and Spilophorini. Relationships and character support of all cassidine tribes are discussed and compared with phylogenies proposed by Borowiec (1995) and Hsiao and Windsor (1999).

The biological account and these phylogenetic results provide an opportunity for identifying some general trends and major innovations in the evolutionary history of Cassidinae. The alteration of the adult head from prognathy to hypognathy and the compaction of the body, legs, and various elytral-locking mechanisms are recurrent themes in adult morphology. Maternal care may have arisen once or twice. Seven trophic guilds are defined here for Cassidine larvae. They arise from two large radiations of leaf-mining and exophagous-feeding, a minor radiation in cryptic rolled-leaf feeding, and small generic and sub-generic specializations in stem mining, leaf scraping, petalophagy, and leaf-shelter chewers. Fecal shield construction and retention appear to be correlated with innovations in life history and in larval and pupal morphology, and they may have played an important role in cassidine diversification.