Bladderwrack

Bernard Courtois discovered elemental iodine in 1811 while extracting sodium and potassium compounds from the ashes of seaweed, specifically Bladderwrack and other related brown algae, which were used as a source material due to their high natural iodine content. Brown algae, like Bladderwrack, are particularly rich in iodine because they concentrate iodide from seawater. - Bernard Courtois – The Discoverer of Iodine