The term seaweed is loosely applied to the many plants found growing in the oceans. Seaweeds, however, are not weeds at all, but marine algae. Marine algae are different from the plants that grow on land because they lack many of the structures typically associated with their terrestrial cousins, such as roots, stems, leaves, and flowers. Yet, both land plants and seaweed are capable of converting the sun's energy into food through the process of photosynthesis. In Fucus and other large brown seaweeds, a structure called the blade contains the specialized cells needed to perform this function. The blade often has a gas bladder, termed a pneumatocyst, attached to it that helps keep the plant near the surface of the water so it can get the sunlight needed for photosynthesis.