Definition of knotted wrack in English:

knotted wrack

noun

mass noun
  • A dark olive-green seaweed with flat branching fronds which bear air bladders, occurring on rocky seashores.

    Ascophyllum nodosum, class Phaeophyceae

    • ‘Its eggs are laid in May and June, primarily on rock surfaces that, at low tide, are covered with the knotted wrack Ascophyllum nodosum.’