Ptychadena nana is a species of frog in the family Ptychadenidae. It is endemic to Ethiopia. It is only known with certainty from its type locality, Arussi Mountains, in the Ethiopian Highlands; these mountains are also referred to as the Arsi Mountains. There is uncertainty regarding reports from elsewhere (in particular, Bale Mountains), which perhaps refer to other, possibly undescribed species. Freilich and colleagues found specimens from the Bale Mountains to be larger than "normal" Ptychadena nana, but that molecular data clustered them with other P. nana. Common names Somali grassland frog and smallest grass frog have been coined for it.