Abstract
The Belostoma plebejum group comprises nine species, and the most evident characteristic shared by all species of the group is a phallus that is strongly curved ventrally. The difficulty in studying its species is much aggravated by the scarcity of identified material in Brazilian collections, and this has negatively impacted phylogenetic studies within the group. We tested the monophyly of the B. plebejum group using discrete and continuous characters under different weighting schemes and inferences. We described B. lanemeloisp. nov. and B. nieserisp. nov. and they served as the basis to study the phylogenetic relationships. A strict-consensus tree recovered under maximum parsimony and with implicit weighting scheme is as follows: (B. parvum, ((B. lanemeloisp. nov., (B. nessimiani, B. nieserisp. nov.)), (B. micantulum var1, (B. micantulum var2, (B. estevezae, ((B. plebejum, (B. minusculum var1, B. minusculum var2)), ((B. nicaeum var1, B. nicaeum var2), ((B. lariversi var1, B. lariversi var2), (B. pygmeum var1, B. pygmeum var2))))))))). The monophyly of the B. plebejum group is corroborated by four non-homoplastic synapomorphies, and the aforementioned condition of the phallus is one of them. We tested the phylogenetic integrity of some species of the B. plebejum group, and only the exemplars of B. micantulum did not constitute monophyletic clades. Comparing the topologies obtained by different approaches clearly showed the presence of different scenarios in terms of heterogeneity of evolutionary rates among characters, but this could also be influenced by the disproportionate number of discrete characters compared with continuous characters.