Changes in Names 

 as a Result of Segregation, Union, or Change in Rank of Taxa 



RULE 17a. An alteration of the diagnostic characters or of the circum- 

 scription of a taxonomic group (taxon) does not warrant a change in its 

 name, except as this may be necessitated by transference of the taxon, by 

 its union with another taxon of the same rank (Rule 19), or by a change of 

 its rank (Rule 22). 



RULE 17b. When a genus is divided into two or more genera, the generic name 

 must be retained for one of them, or (if it has not been retained) must be 

 re-established. When a particular species was originally designated as the 

 type, the generic name must be retained for the genus including that species. 

 When no type was designated, a type must be chosen. 



The same rule is applied when a subgenus is divided into two or more 

 subgenera. 



RULE 17c. The name of a taxonomic group must be changed if the nomen- 

 clatural type of the taxon is excluded. 



ANNOTATIONS 



Rule 17a. There is no warrant for changing the name of a taxon 

 because the boundaries (circumscription) of the taxon are changed. 

 The addition of new species to a genus may require a modification 

 of the description (tabulation of diagnostic characters) of the genus, 

 but not a change of name. For example, the genus Pseudomonas 

 Migula 1894 is defined by some authors to include polar flagellate 

 plant pathogens with yellow, non-diffusing pigment; others use the 

 generic name Xanthomonas Dowson 1939 for the latter. Contraction 

 or expansion of the boundaries of the genus itself is no reason for 

 changing the name as long as the type species is retained within the 

 genus. 



Rule 17b. Example: When Donker (1926) proposed and named a 

 new genus Aerobacillus to include those species of the genus Bacillus 

 which are aerogenic, he correctly retained the generic name Bacillus 

 for that portion which included the type species Bacillus subtilis 

 Cohn. Winslow and Rogers (1906) divided the genus Staphylococcus 

 Rosenbach (1884) into two genera named Aurococcus and Albo- 

 coccus. One of the genera should have retained the name Staphylo- 

 coccus, that containing the type species. 



The corresponding Article in the Botanical Code has essentially 

 the same wording. 



The Zoological Code provides that when two or more restricted 

 genera are formed by the division of a genus, the available name 



[81] 



