^aCompiled after Benson et al. (2004) and Swensen (1996).

^bAccording to the classification of the Angiosperm Phylogeny Group (APG 1998); all of these orders fall in the “Eurosid I” group of eudicots.

^cThe number of genera within the family is listed along with the number of genera nodulated. Not all genera within a family are capable of nodulation.

^dThe Frankia cluster refers to the clusters of Frankia strains in Figure 1 typically found in root nodules of each plant genus. 1, alder and casuarina strains; 3, elaeagnus strains; 2, rosaceous strains; ND, not determined; (3) indicates rare detection of an elaeagnus strain in a nodule or in surface layers of a nodule (Benson et al. 2004).

(NA) North America; (SA) South America.