What Kinds of Seaweed Are There?

All marine plants can be classified as seaweed. The many different species are broken into three main groups: green algae (Chlorophyta), red algae (Rhodophyta) and brown algae (Phaeophyta). Harvesting seaweed is a major economic source for countries such as Japan, Korea and China.

Green Algae (Chlorophyta)

• Green algae is a common type of seaweed.

  Many types of green seaweed are not true plants at all. They share characteristics with single- and multiple-celled organisms. Of the 7,000 known species, only 700 are found in aquatic environments. They are common in shallow water and tidal pools, growing on rocks or other porous surfaces. Chlorophyta can be found in everything from vitamin supplements to mascara, and are even used as a dressing for wounds and other hypoallergenic applications.

Brown Seaweed (Phaeophyta)

• Brown seaweed is harvested for food and manufacturing.

  This group contains the largest and most complex forms of aquatic plants. Giant kelp is one of the largest in this category. Kelp is used for everything from cosmetics to medical applications, and is considered important to coastal peoples around the world, both as a food source and an economic product. Some kelp species can grow as much as 20 feet per day and reach a total length of 90 feet. Also referred to as brown algae, this family of seaweed has 1,500 species, most of which are aquatic. Brown algae grow in huge underwater forests that provide shelter and food for a plethora of other marine life, including fish and shrimp.

Red Algae (Rhodophyta)

• Red Algae is common on coral reefs.

  Red algae comprises over 4,000 species, and most are found only in water. It is the most populous family of aquatic plants, totaling more than green and brown algae together. Red algae has evolved to fill different niches, even acting as parasites on other species. As the plants die, they leave behind an articulated, branched network of calcium carbonate deposits, adding to the growth of coral reefs.