Seaweed is a name commonly used for the multicellular marine algae. Some seaweeds are microscopic, such as the phytoplankton that live suspended in the water column and provide the base for most marine food chains. Some are enormous, like the giant kelp that grow in abundant “forests” and tower like underwater redwoods from their roots at the bottom of the sea. Most are medium-sized, come in colors of red, green, brown, and black, and randomly wash up on beaches and shorelines just about everywhere. Seaweed usually has a basal disk, called a holdfast, and a frond of varying length and shape, which often resembles a plant in having stemlike and leaflike parts.