bladder wrack vs rockweed

bladder wrack

noun
  • Fucus vesiculosus, seaweed widespread in the cool waters of the Atlantic and Pacific. 

  • Nereocystis luetkeana, kelp common on the northeastern Pacific coast. 

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 bladder wrack and rockweed occurred in a corpus of books? (source: Google Ngram Viewer )