This amazing species of Adiantum is endemic to the humid forests of southern Bahia, Brazil. It is extremely rare and endangered, being known from less than five localities. Adiantum diphyllum is characterized by its continuous linear sori and copiously anastomosing veins, which are uncommon characters in the genus. The most similar species is A. adiantoides (J. Sm.) C. Chr. To know learn more about them, read Sundue & Prado (2005). Brittonia 57(2): 123-128.