Young JM. The genus name Ensifer Casida 1982 takes priority over Sinorhizobium Chen et al. 1988, and Sinorhizobium morelense Wang et al. 2002 is a later synonym of Ensifer adhaerens Casida 1982. Is the combination "Sinorhizobium adhaerens" (Casida 1982) Willems et al. 2003 legitimate? Request for an Opinion. Int J Syst Evol Microbiol 2003; 53:2107-2110.
Euzeby JP. Notification list. Notification that new names and new combinations have appeared in volume 53, part 6 of the IJSEM. Int J Syst Evol Microbiol 2004; 54:309-311. Notes:
Emendation accompanied by the proposal of 9 new species in the genus.
According to J.M. Young , there is no justification in the Bacteriological Code (1990 Revision) for this step. This author  proposed that Ensifer adhaerens Casida 1982 be the legitimate nomenclature and requested for a Judicial Opinion.
According to the "Subcommittee on the taxonomy of Agrobacterium and Rhizobium" , the genus Ensifer and the genus Sinorhizobium belong to a single taxon and Ensifer has priority. However, there are good reasons for retaining the name Sinorhizobium over Ensifer; hence, a case to this effect needs to be prepared for consideration by the Judicial Commission. In July 2003, Willems et al.  propose the new combination "Sinorhizobium adhaerens" (Casida 1982) Willems et al. 2003 and put forward a Request for an Opinion to the Judicial Commission regarding the conservation of "Sinorhizobium adhaerens" over Ensifer adhaerens. A new name or new combination subject to a Request for an Opinion should not be considered as validly published unless the Judicial Commision votes to approve the Request.
According to the "Subcommittee on the taxonomy of Agrobacterium and Rhizobium" , phylogenies based on several core genes suggest that Ensifer adhaerens and Sinorhizobium morelense form a sister clade to the rest of the Sinorhizobium species [Martens et al., Int. J. Syst. Evol. Microbiol., 2007, 57, 489-503]. If confirmed, this could be a basis for retaining Sinorhizobium and Ensifer as distinct genera.
At its meetings in August 2008 , the "Subcommittee on the taxonomy of Agrobacterium and Rhizobium" did not disagree with the interpretation of the Judicial Commission. However, the subcommittee disagrees with the justification. The transfer of the members of the genus Sinorhizobium to the genus Ensifer would cause great confusion in the scientific community. At a session of the 8th European Nitrogen Fixation Conference on 31 August 2008, an overwhelming majority of those present indicated that they were not in favour of changing the name from Sinorhizobium to Ensifer. In 2010, J.M. Young  comments and disapproves the decision of the subcommittee.
At its meetings in July 2005 at the IUMS Congress in San Francisco, the Judicial Commission of the International Committee on Systematics of Prokaryotes  ruled on the Requests for an Opinion of Willems et al.  and J.M. Young . The genus name Ensifer Casida 1982 has priority over the genus name Sinorhizobium Chen et al. 1988, and the two names have been shown by Willems et al.  to be synonyms. It was generally felt that the transfer of the members of the genus Sinorhizobium to the genus Ensifer would not cause confusion and, therefore, the Judicial Commission  denied the request to conserve the genus name Sinorhizobium Chen et al. 1988 over the genus name Ensifer Casida 1982. A direct result of this ruling is that the name "Sinorhizobium adhaerens" Willems et al. 2003 is also not validly published, since it was proposed in anticipation of this Opinion .
The type species of this genus has alternatively been placed in the genus Sinorhizobium Chen et al. 1988.Publication:
Willems A, Fernandez-Lopez M, Munoz-Adelantado E, Goris J, De Vos P, Martinez-Romero E, Toro N, Gillis M. Description of new Ensifer strains from nodules and proposal to transfer Ensifer adhaerens Casida 1982 to Sinorhizobium as Sinorhizobium adhaerens comb. nov. Request for an opinion. Int J Syst Evol Microbiol 2003; 53:1207-1217.
Number of child taxa with a validly published and correct name: 20 Number of child taxa with a validly published name, including synonyms: 21 Total number of child taxa: 25