ABSTRACT
Actinorhizal plants are nonlegumes that form root nodules in symbiosis with the N2-fixing actinomycete Frankia (Torrey and Tjepkema, 1979). These symbioses occur in a phylogenetically diverse group of plants; at least 24 genera in eight families are reported to nodulate with Frankia (Table 1). They include trees, such as Casuarina and Alnus, shrubs (e. g., Coriaria and Purshia) , and occasionally perennial herbs (Datisca spp.). Compared to the vast group of N2-fixing Leguminosae (Allen and Allen, 1981), there are relatively few species of actinorhizal plants. However, this numerical inferiority is offset by the ability of many to grow in harsh, infertile environments (Bond, 1983).
