However, a study was published that year based on fieldwork conducted from 1999 to 2001 which found that individuals from the Udzungwa and Uluguru mountains were consistently distinguishable from those found in the Usambara Mountains further north (where the type specimen of the Usambara torrent frog was collected).

Therefore, the southern form was described as a new species and given the scientific name Arthroleptides yakusini, with the specific name being derived from the Swahili words "ya kusini", meaning "of the south" and referencing how this species occurs south of the range of the Usambara torrent frog.

The following cladogram shows the position of the southern torrent frog among its closest relatives according to said study:[6] A. martiensseni A. sp.

[7] Though sometimes claimed to also be found in the Nguru Mountains,[1] molecular evidence suggests this population actually represents a separate, currently unnamed species within the same genus.

[8] The southern torrent frog mostly inhabits rocky streams surrounded by montane forest, with a preference for mature forest (though it may tolerate open woodland habitats more than the related Usambara torrent frog), and has an estimated extent of occurrence of 3,113.18 km2 (1,202.0 sq mi).