This alga is common in the lower intertidal from Long Island Sound to Labrador. It has flat blades that are often forked at the ends. Underwater it is deep purple-red, with a slight iridescent blue tinge. Out of the water (ie. washed up in the wrack line) it tends to fade to pinkish purple and sometimes white or yellow. It is a crucial representative species of the lower rocky intertidal. This alga is used for food, especially in the preparation of puddings. It contains the chemical carrageenan, which is a gel-like thickener used in dairy products, toothpaste, and many other products. Carrageen(an) is an Irish word that may derive from Carigeen Head in County Donegal, but there are many place names with the name Carrag(h)een or Carrigeen (from carraigín: diminutive of rock). Personally it is one of my favorite algae, because it is beautiful underwater and a welcome relief on feet when exploring the intertidal.