Abstract Alternaria brown spot is a leaf disease of annonaceous plants recently assigned to Alternaria alternata , a species in section Alternaria . Given the diversity in Alternaria section Alternaria and the economic importance of annonaceous plants for Brazilian fruit producers, we sought to identify the aetiological agents of Alternaria brown spot in Brazil and evaluate their aggressiveness and host associations. In addition, we compared different methods of species delimitation within section Alternaria . According to several species delimitation methods, the causal agents of Alternaria brown spot in Brazil were assigned A . alternata (clades 2 and 5), A . longipes ‐like ( A . gossypina and Alternaria sp. [LM 353]), A . tomato ‐like ( Alternaria sp. [LM 281; LM 295; LM 267], Alternaria sp. [LM 269; LM 294; LM 306] and Alternaria sp. [LM 272]), A . jacinthicola and a new species, A . annonacearum . All lineages were pathogenic to sugar apple and soursop, though less aggressive on the latter, irrespective of the host from which they were isolated. This study brings information that may help both researchers and fruit producers to distinguish Alternaria brown spot from other fungal diseases on annonaceous plants and ultimately develop better management approaches.