The etymology of the species name derives from the Portuguese word sul, meaning "south", and pertains to its southern geographic range.
References
^ abLeite, Yuri L. R.; Christoff, Alexandre U.; Fagundes, Valéria (2008-08-15). "A New Species of Atlantic Forest Tree Rat, Genus Phyllomys (Rodentia, Echimyidae) from Southern Brazil". Journal of Mammalogy. 89 (4): 845–851. doi:10.1644/07-MAMM-A-343.1. ISSN0022-2372.