Red seaweeds are a favorite object for scientists to study because they are specialized plants with unusual properties. Polysiphonia is one such seaweed. It consists of long thin branches with lots of fine side branches. When looked at under a microscope, you see its typical complex tube-like structure. Some species are black-brown, others are bright red. Sometimes Polysiphonia forms thick mats, providing a good bottom for other seaweeds to attach to. Other times, it uses seaweeds or rocks for its own base. One species always grows on knotted wrack (see photo), but is rarely found nowadays. Most Polysiphonias grow in the lower tidal zone. They grow just as well in rough as calm and salty as brackish water.