Almost 200 years of anthocyanin research: What we know, what we assume and what remains unknown.

Flavonoids are frequently presented as health-beneficial plant metabolites, and their subclass anthocyanins is best known for striking flower colours. The biosynthesis of flavonoids has been studied for decades and has developed into a model system in plant biology. Despite thousands of publications about this pathway, there are still open questions about fundamental aspects of anthocyanin biosynthesis. Here, we review the evolution of anthocyanin biosynthesis and highlight key open questions-some of which are sitting in plain sight.