Mastrocarpus stellatus is a red algae mainly found on rocky coasts in the North Atlantic region. It has a reddish to brown color with cartliginous laminae that usually have a leathery texture and can become dark when dehydrated. It is a source of carrageenan, a type of polysaccharide used as a thickener and stabilizer in foods and pharmaceuticals. This algae prefers rocky coastal areas, where it is often exposed to the air during low tide.