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.

The synonymy of the genera Ensifer and Sinorhizobium was recently reported, but it was proposed that the later-named genus, Sinorhizobium, take priority in nomenclature. There is no justification in the International Code of Nomenclature of Bacteria (Prokaryotes) for this step; Ensifer is the correct name of the genus, with Ensifer adhaerens as the type species. Species previously allocated to Sinorhizobium are here proposed as the new combinations Ensifer arboris, Ensifer fredii, Ensifer kostiensis, Ensifer kummerowiae, Ensifer medicae, Ensifer meliloti, Ensifer saheli, Ensifer terangae and Ensifer xinjiangensis. Sinorhizobium morelense was proposed in 2002 [Wang, E. T., Tan, Z. Y., Willems, A., Fernández-López, M., Reinhold-Hurek, B. & Martínez-Romero, E., Int J Syst Evol Microbiol 52, 1687-1693, 2002], but a consideration of all published data indicate that it is a nitrogen-fixing genomovar and later heterotypic synonym of Ensifer adhaerens. A Request for an Opinion is made as to whether or not the combination "Sinorhizobium adhaerens" (Casida 1982) Willems et al. 2003 is legitimate.