Figure 1

Chronogram of the nitrogen-fixing clade.
Dating analysis was performed using PL method. Green indicates rhizobial lineages; red represents actinorhizal nitrogen-fixing lineages (numbered 1–9); grey represents unknown; black represents no nitrogen-fixing symbiosis. Green box indicates the nodule morphological characteristics of rhizobial nitrogen-fixing plants and their symbiotic partners and red box indicates that of actinorhizal nitrogen-fixing plants and their symbiotic partners.