The study surveyed 246 plant and algal genomes to examine the evolution and duplication of the chlorophyllide a oxygenase (CAO) gene, revealing multiple independent duplications, especially in land plants. It also traced the emergence and conservation of the CAO regulatory degron sequence, showing poor conservation in chlorophytes, emergence in charophytes, and high conservation in embryophytes, thereby illuminating the evolutionary history of chlorophyll b biosynthesis.