The cryptochromes are a group of pigments found in virtually all animals, plants and many bacteria. They consist of a flavin (a derivative of vitamin B2) folic acid and protein. Cryptochromes have been suggested to form the basis of light-dependent magnetic compass orientation in birds. However, to function as magnetic compass sensors, the cryptochromes of migratory birds must possess a number of key biophysical characteristics. Like all pigments, they get their colour by absorbing light at specific wavelengths. Cryptochromes represent an entirely different class of photopigments, belonging to the photolyase blue-light receptor family. Unlike the retinaldehyde-based opsins, cryptochromes use two light-absorbing cofactors - flavin adenine dinucleotide and methenyltetrahydrofolate. In Arabidopsis, cryptochrome 2 (cry2) is involved primarily in the control of flowering time and in photomorphogenesis under low-fluence light.