Kelp 
(Fucus vesiculosus)

    This is a seaweed and brings with it the nutritional properties of the sea from which it is harvested. For this reason it is high in valuable minerals but also prone to marine pollution, so care should be taken in sourcing it. Kelp is highly nutritious, making it a valuable dietary supplement. It is emollient and usable as a poultice. It is rich specifically in potassium and iodine. Calcified seaweed makes a very good land top-dressing in place of chemical fertilizers, providing humus and mineral nutrients in a valuable ‘slow release’ balance. It is of particular use in goitrous conditions or in areas of the country known to be short in iodine.

Notes: Check out one of the commercial supplements containing kelp, the "Source".