This species of the unspotted P. albipinna species group is distinguished by the following set of characters: long mental barbel, about 15-20% SL without terminal expansion (vs. short and blunt in P. immaculata, with terminal expansions in albipinna and dewitti); shallow head and slender trunk with a slight taper to caudal peduncle (vs. deeper heads and more abruptly tapered bodies for the 3 former species); middle lateral line pores 8-13 (vs. indistinct in albipinna, 12-29 with most 16-29 in immaculata and 17-19 in dewitti) ; divergence in mitochondrial ND2 gene between stewarti and immaculata not available from albipinna and dewitti (Ref. 84672).