LAUSR

Leaf‐cutting ants (genera Acromyrmex and Atta) are the most important herbivores in the Neotropical region. Within the genus Acromyrmex, the species and subspecies Acromyrmex striatus, Acromyrmex silvestrii subsp. silvestrii and Acromyrmex silvestrii subsp. bruchi are morphologically similar to one another but differ from the rest of their congeners. Recent studies have suggested that Ac. striatus belongs to a currently undescribed leaf‐cutting ant genus. Herein, we propose a new phylogenetic hypothesis for leaf‐cutting ants based on five nuclear genes (wg, LW Rh, EF1αF1, EF1αF2 and Top1) and describe a new genus. We used colonies of Ac. striatus, Ac. silvestrii silvestrii and Ac. silvestrii bruchi collected from Brazil, Argentina, Uruguay and Bolivia, covering most of their known distribution. We constructed a molecular phylogenetic hypothesis for these three taxa using sequences from the mtDNA COI gene. The retrieved phylogenetic tree reveals that Ac. striatus, Ac. silvestrii silvestrii and Ac. silvestrii bruchi form a well‐supported clade (P.P. = 1). Through analyses of molecular phylogenetic and morphological data, we propose a new genus of leaf‐cutting ant, Amoimyrmex Cristiano, Cardoso & Sandoval, gen. nov., redescribe the species Amoimyrmex striatus (Roger, 1863) comb. nov. and Amoimyrmex silvestrii (Emery, 1905) comb. nov., and elevate Ac. silvestrii bruchi to the level of species as Amoimyrmex bruchi (Forel, 1912) comb. nov. et stat. rev.. We also provide information on the geographic distribution of Amoimyrmex, an illustrated identification key for its taxa and descriptions of all the known castes of each species, including diagnostic characteristics, high‐quality images and distribution maps. We believe that the results of this study contribute substantially to taxonomic knowledge of leaf‐cutting ants and reaffirm the complex evolutionary history of the group.