3.3.1 Some vascular plants establish nitrogen-fixing symbioses o There are three major types of nitrogen-fixing symbioses o 1)Gram-negative bacteria, the rhizobia, form associations with numerous legume host plants(Fabaceae) and at least one non legume, Parasponia(ulmaceae) o 2)Gram-positive actinomycete genus( Frankia)and a diverse group a dicots, generally trees or woody shrubs from about 60 genera in 9 families, including alder(Alnus), myrtle( Myrica), Casuarina and Ceanothus o 3) Symbioses exist between cyanobacteria and a diverse array of plants: dicots(e.g, Gunnera), cycads, ferns,liverworts, and hornworts. Azolla, a water fern, associates symbiotically with the cyanobacterium3.3.1 Some vascular plants establish nitrogen-fixing symbioses ⚫ There are three major types of nitrogen-fixing symbioses. ⚫ 1) Gram-negative bacteria, the rhizobia, form associations with numerous legume host plants (Fabaceae) and at least one non legume, Parasponia(Ulmaceae). ⚫ 2) Gram-positive actinomycete genus ( Frankia) and a diverse group a dicots, generally trees or woody shrubs from about 60 genera in 9 families, including alder(Alnus), myrtle(Myrica), Casuarina, and Ceanothus. ⚫ 3) Symbioses exist between cyanobacteria and a diverse array of plants: dicots (e.g.,Gunnera), cycads, ferns,liverworts, and hornworts. Azolla, a water fern , associates symbiotically with the cyanobacterium