bladderwrack

noun

1. a common seaweed, Fucus vesiculosus, found in cold marine waters, having narrow brownish fronds with air-filled vesicles.

noun

1. any of several seaweeds of the genera Fucus and Ascophyllum, esp F. vesiculosus, that grow in the intertidal regions of rocky shores and have branched brown fronds with air bladders