Actinorhizal Plants

Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinobacteria Frankia. 

Actinorhizal plants are dicotyledons distributed among 3 orders, 8 families and 24 genera.  These three orders form a single clade within the Rosids, which is a sister taxon to the other major nitrogen-fixing order, the Fabales.  Not all plants in this clade are actinorhizal, however. 

Order	Family	Genus
Cucurbitales	Coriariaceae	Coriaria
	Datiscaceae	Datisca
Fagales	Betulaceae	Alnus
	Casuarinaceae	Allocasuarina Casuarina Ceuthostoma Gymnostoma
	Myricaceae	Comptonia Myrica
Rosales	Elaegnaceae	Elaeagnus Hipophae Shepherdia
	Rhamnaceae	Colletia Discaria Kentrothamnus Retanilla Talguenea Trevoa Ochetophila Ceanothus
	Rosaceae	Cercocarpus Chamaebatia Cowania Dryas Purshia

 

 

Actinorhizal plants are found on all continents except for Antarctica. Their ability to form nitrogen-fixing nodules confers a selective advantage in poor soils. Most actinorhizal plants are therefore pioneer species that colonize young soils where available nitrogen is scarce. 

Other nitrogen fixing families include Trema ( Parasponia ), a tropical genus in the family Cannabaceae, which are able to interact with Rhizobia.