Ah interesting I knew about the American Code and indeed later disputes between US and European taxonomists e g over Hippeastrum vs Amaryllis Not sure where if anywhere Canadian taxonomists stood Whoever wrote the bit on the IPNI page here seems to be of the view that the Kew Rule was knowingly deviant by writing Jackson 1887 described and his use of this rule my italics I can t find what Jackson 1887 refers to Jackson may have felt it necessary to defend the Kew Rule given that de Candolle had objected in 1877 perhaps de Candolle in 1888 was responding to this piece by Jackson There is a logic to Jackson s argument Suppose the names A b X and C d Y are independently published for the same species homo or heterotypically and it seems that C perhaps narrower in concept is the better genus then someone else has to correct C d to C b X Z so there are now 3 synonyms to keep track of instead of 2 under the Kew rule On the other hand keeping the epithet constant is very helpful in researching synonyms