Cycas possesses small specialised roots called coralloid roots which are associated with N2-fixing cyanobacteria . Cyanobacteria (Blue-green algae) are prokaryotic and autotrophic (photosynthetic) organisms . In contrast, Cicer (chickpea) and Pisum (pea) are legumes associated with the symbiotic bacterium Rhizobium, which is heterotrophic . Alnus is associated with Frankia, which is also not autotrophic in the same sense as cyanobacteria.