 They have not been found in flowers, unless the brown and black pigments in the involucrum of certain compositae are found to be of the phlobaphen type.In bark, phlobaphenes accumulate in the phellem layer of cork cambium, part of the suberin mixture.Many cinchona barks contain a particular tannin, cinchotannic acid, which by oxidation rapidly yields a dark-coloured phlobaphene called "red cinchonic", "cinchono-fulvic acid" or "cinchona red".