The placement of "B. sceptrum" (Sceptre Banksia) in this series was initially tentative, as George felt that "in some respects it also shows a relationship to the series "Cyrtostylis"". "B. aemula" (Wallum Banksia) was also flagged as anomalous in having a conical pollen-presenter, and "B. pilostylis" (Marsh Banksia) was noted as the only species outside the series that has a hairy pistil. Overall, George accepted that the resultant series was "somewhat heterogeneous", but argued that the species had enough in common to warrant grouping them together. Since species of "B." ser. "Orthostylis" occur in both western and eastern Australia, George suggested that it had evolved early, and was widespread across southern Australia before aridification and marine incursion established the Nullarbor Plain as a barrier to genetic exchange.