X-ray analysis reveals why anthocyanin found in red roses turns other flowers a brilliant blue

It is known that the colours of many flowers are produced by anthocyanin, which has 6 different types of structure; a cyanidin-type anthocyanin is responsible for the red in roses, while most blue flowers have delphinidin-type anthocyanin. However, the same cyanidin-type anthocyanin makes roses red but cornflowers blue. The phenomenon has so far not been entirely explained. A Japanese group led by Professor K. Takeda (Tokyo Gakugei University, Koganei, Tokyo) recently carried out detailed X-ray analysis and clarified that a complex of six molecules each of anthocyanin and flavone, with one ferric iron, one magnesium and two calcium ions is responsible for the blue in cornflowers. For more information, see the paper, "Phytochemistry: Structure of the blue cornflower pigment", M. Shiono et al., Nature, 436, 791 (2005).