bladderwrack vs rockweed

bladderwrack

noun
  • Fucus vesiculosus, a seaweed in which iodine was first discovered. 

rockweed

noun
  • Fucus vesiculosus, a similar seaweed also known as bladderwrack. 

  • Ascophyllum nodosum, a seaweed also known as knotted wrack. 

How often have the words bladderwrack and rockweed occurred in a corpus of books? (source: Google Ngram Viewer )