How do cycad roots form coralloid structures?

Cycadophytes develop coralloid roots through the growth of short-branching, apogeotropic (upward-growing) roots. These specialized structures are characterized by an irregular, beady appearance.1

The formation of these roots is closely linked to a symbiotic relationship with cyanobacteria. These microorganisms inhabit the coralloid roots, where they perform nitrogen fixation. In this mutualistic association, the cyanobacteria convert atmospheric nitrogen into compounds that the plant can utilize, while the root tissues facilitate the production of beneficial amino acids such as asparagine and citrulline.1