Riley described the gall of this and several other leaf-galling species but never formally described the adults, which Riley (1890) said so closely resembled
P. celtidismamma that "they can only be distinguished with difficulty". These two facts caused subsequent authors to treat Riley's names as either
nomina nuda or as synonyms of
P. celtidismamma. However, as D.B. Thomas (2011) points out, names published prior to 1931 based on descriptions of galls are indeed valid under the ICZN, and recent studies by Yang and Mitter (1994)
(2) concluded that
P. celtidismamma was indeed a cryptic-species complex, though more work needs to be done in order to fully understand which of Riley's species are indeed valid
(3).