The genus Aleixus McDonald is reviewed and a new species described. The genus was monotypic and known from a single female from Brazilian Amazonia. The new species Aleixus tobyschuhi described from southern Brazil, greatly extends the distribution of Aleixus. A cladistic analysis, including 30 morphological characters and 18 taxa, was performed using TNT with the implicit enumeration algorithm, with three weighting schemes: equal (EW), successive approximation (SW), and implied weighting (IW). Analysis under EW resulted in four cladograms (L  =  74, CI  =  60, RI  =  78). Analyses under SW and IW resulted in one most parsimonious cladogram, with fit varying from 20.4 (K  =  0.64) to 26.6 (K  =  5.80). The cladogram obtained under differential weighting schemes is included in the set of cladograms found under EW. The monophyly of the tribe Procleticini and genus Aleixus were recovered in all analyses. Non-ambiguous synapomorphies for Aleixus include antennal segment II longer than antennal segment I, and humeral angles developed in spatular projections, dorsally bifid. Non-ambiguous synapomorphies of Procleticini are metasternum sulcate, ventral rim of pygophore with a medial U-shaped emargination and with 1 1 process with different degree of development, and gonocoxites 8 smaller than laterotergites 9. A hypothesis of relationships among Procleticini genera was possible only under IW analysis. Two main clades were recognized: clade A, including the genera Brepholoxa Van Duzee, Dendrocoris Bergroth, Procleticus Berg, and Thoreyella Spinola; and clade B, including the genera Aleixus, Odmalea Bergroth, Parodmalea Rider, and Pseudobebaeus Distant.