Auricularia auricula-judae is a fungus found growing on dead Sambucus. This fungus contains iron, calcium, and also iron. The fungus is foraged for worldwide and can be rehydrated once dried. 

The Chinese use the fungus in soups, other food products. If fried, it can literally 'jump around' due to the water pockets inside the fungus. Other names include 

Judas ear, Jews ear, and Jews meat The Judas ear derive from the story that Judas hung himself on the Sambucus tree, thus leaving behind the only sign of him, his ear. The Jews Meat name actually comes from antisemitism during the middle ages.