What is an anthocyanin? What compounds are they related to? Anthocyanins are water-soluble scarlet, magenta, purple and blue pigments that colour the fruit and flowers of many plants. They also provide the red colours of many autumn leaves. They are flavonoids, formed by phenylpropanoid metabolism from phenylalanine. In addition to colouring specific plant organs, often to attract pollinators and dispersers, they may serve to protect photosynthetic tissues from oxidative stress induced by light under stressful conditions. They are synthesised by gymnosperms and most angiosperms except the Caryophyllales (beets, cacti, Bougainvillia, Amaranthus), which synthesise the unrelated betalain pigments from tyrosine instead.