Citrus sinensis caffeine synthesis pathway.
[Convergent Biochemical Pathways for Xanthine Alkaloid Production in Plants Evolved from Ancestral Enzymes with Different Catalytic Properties](https://pmc.ncbi.nlm.nih.gov/articles/PMC8233510/)
[Convergent evolution of caffeine in plants by co-option of exapted ancestral enzymes](https://pmc.ncbi.nlm.nih.gov/articles/PMC5035902/)