R. brockwellii (brock.well’i.i N.L. masc. gen. n. brockwellii, of Brockwell, to honour John Brockwell, who isolated the type strain and made major contributions to the development of rhizobial inoculation in Australia). The type strain is Brockwell CC275eT=ICMP 2163T = NZP 561T=LMG 6122T= HAMBI 13T = ATCC 35181T. It was isolated from a nodule on Trifolium repens growing near Cape Grim, Tasmania, Australia in 1966 by John Brockwell (pers. comm.) and has been a widely used clover inoculant in Australia and New Zealand [23]. The genome sequence [23] is INSDC accession GCA_000769405.2 and the 16S rRNA gene sequence is OQ226180. This description is based on 37 isolates with published genome sequences (Table S1). They were isolated in Denmark, Russia, Belarus, Colombia and Australia. The species has also been found in the UK [3]. Members of this species have ANI above 96 % with the type strain, and, in a phylogeny based on core gene sequences, group with the type strain in a clade that excludes members of other species. The species is genospecies A of the Rhizobium leguminosarum species complex, as defined by Young et al. [6] and s__Rhizobium leguminosarum_E in the Genome Taxonomy Database release 07_RS207 [24]. The type strain has a POCP of 85.27 % with USDA 2370T, the type strain of R. leguminosarum, the type species of the genus. This confirms that the novel species is a member of the genus Rhizobium. Furthermore, the sequence of the 16S rRNA gene of the type strain is identical to that of USDA 2370T. This 16S rRNA sequence is also found in 31 of the other genomes of strains of R. brockwellii, but a further five genomes share a single substitution, C1076T [6]. The genome size range is 6.97–7.40 Mb (that of the type strain is 7.12 Mb). The genomic DNA G+C content range is 60.64–60.88 % (type strain 60.88 %). In addition to the two chromids that are universal in the Rlc (plasmid types Rh01 and Rh02), strains of R. brockwellii carry plasmids of types Rh03 (37 out of 37 strains), Rh05 (37 out of 37) and Rh06 (36 out of 37). Other plasmids are present in some strains, though Rh07 has not been detected. Table 1 lists 22 genes that are present in 97–100 % of strains of R. brockwellii but are absent from the sister species gsH and are rare elsewhere in the Rlc (<5 % of genomes). In the type strain, they are predominantly carried on the chromosome or the Rh01 chromid (pRltCC275eF). These genes are diagnostic characteristics of the species. All 37 isolates characterised so far are sv. trifolii and nodulate clovers (Trifolium spp.), but this should not be considered a defining feature of the species.

The type strain is Brockwell CC275eT=ICMP 2163T = NZP 561T=LMG 6122T= HAMBI 13T = ATCC 35181T