Actinorhizal

Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinobacteria Frankia. This association leads to the formation of nitrogen-fixing root nodules.

Actinorhizal plants are dicotyledons distributed among three angiosperm 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. All actinorhizal species are trees or shrubs, except for the genus Datisca.

Many are common plants in temperate regions like alder, bayberry, sweetfern, Avens, mountain misery and Coriaria. Some Elaeagnus species and Sea-buckthorns produce edible fruit. In tropical regions, Casuarinas are widely cultivated.

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 like moraines, volcanic flows or sand dunes. Being among the first species to colonize these disturbed environments, actinorhizal shrubs and trees play a critical role, enriching the soil and enabling the establishment of other species in an ecological succession. Actinorhizal plants like alders are also common in the riparian forest.

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