Fig. 4.

The flavodoxin gene was lost along the evolution of Viridiplantae during the colonization of terrestrial habitats by streptophyte algae. The hypothesis assumes that plants originated from freshwater streptophytes which already lacked Fld. Cyanobacteria and algae thriving in iron-deficient oceanic environments usually contained the fld gene, whereas coastal and freshwater counterparts evolved in a habitat in which iron was plentiful and bioavailable, and the role of Fld as a backup of Fd was presumably not required. Typical cyanobacteria, algae, and plants are depicted schematically. The negative correlation between iron levels and Fld presence is shown in the bottom. They are intended to represent tendencies and do not depict actual iron/Fld contents.