Bladderwrack is a common brown seaweed of the north Atlantic and Pacific rocky shores, made from Fucus vesiculosus and named for the paired, pea-sized air bladders that dot its forking, olive-brown fronds. Foraged between the tide lines, it is used as a mineral-rich broth and pot-herb seaweed and, more famously, in the hot seaweed baths of the Atlantic coast.