A systematic review of the endangered genus Petrocerus Callaghan, 1979 (Lepidoptera: Riodinidae) reveals two new overlooked species

Taxonomy is a fundamental discipline for biology, especially for the effective conservation of biodiversity. Here, we performed a review of Petrocerus Callaghan, 1979, an endangered and hitherto monotypic butterfly genus endemic to the Brazilian Atlantic Forest. Museomics revealed a new, overlooked and potentially endangered species from southern Brazil (Santa Catarina), Petrocerus kaingang Dias, Dolibaina & Kaminski sp. nov. , while field work conducted on hilltops and genomic data revealed a new species from southeastern and northeastern Brazil (Espírito Santo and Bahia), Petrocerus ardilosa Dias, Dolibaina & Kaminski sp. nov. Additionally, a lectotype is designated for Calydna catiena Hewitson, 1875. Genomic data confirm the classification of Petrocerus in Theopina (Nymphidiini), a subtribe that includes species that live in symbiosis with ants. The presence of greasy wings, an annual life cycle and an apparent association of adults with bamboo patches (in P. catiena and P. ardilosa sp. nov. ) suggest that these butterflies have complex life cycles with ants and trophobionts, as observed in one species of the sister genus Pseudotinea Hall & Callaghan, 2003. Unravelling these aspects of the natural history of Petrocerus is the next step towards the conservation of this rare group of butterflies.