Green Algae (Chlorophyta)

Green algae can be used as food by sea life and humans

Green algae patterns on exposed rock at low tide, Gros Morne National Park, Ontario, Canada
Altrendo Nature/ Stockbyte/ Getty Images

Chlorophyta are commonly known as green algae and sometimes, loosely, as seaweed. They grow primarily in freshwater and saltwater, although some are found on land. They may be unicellular (one cell), multicellular (many cells), colonial (a loose aggregation of cells), or coenocytic (one large cell). Chlorophyta converts sunlight to starch that is stored in cells as a food reserve.

Green Algae Characteristics

Green algae have dark- to light-green coloration that comes from having chlorophyll a and b, which they have in the same amounts as "higher plants," the plants, including seed plants and ferns, that have well-developed vascular tissues that transport organic nutrients. Their color is determined by the amounts of other pigmentation, including beta-carotene (yellow) and xanthophylls (yellowish or brownish).

Like higher plants, they store their food mainly as starch, with some as fats or oils. In fact, green algae might have been the progenitors of the higher green plants, but that is the subject of debate.

Chlorophyta belong to the kingdom Plantae. Originally, Chlorophyta referred to a division within the Plantae kingdom composed of all green algae species. Later, green algae species living predominantly in seawater were classified as chlorophytes (i.e., belonging to Chlorophyta), while green algae species thriving mainly in freshwater were classified as charophytes (i.e., belonging to Charophyta).

The AlgaeBase database lists about 4,500 species of Chlorophyta including 550 species of Trebouxiophyceae (mostly on land and in freshwater), 2,500 species of Chlorophyceae (mostly freshwater), 800 species of Bryopsidophyceae (seaweeds), 50 species of Dasycladophyceae (seaweeds), 400 species of Siphoncladophyceae (seaweeds), and 250 marine Ulvophyceae (seaweeds). Charophyta includes 3,500 species allocated to five classes.

Habitat and Distribution of Green Algae

The habitat of green algae is diverse, ranging from the ocean to freshwater. Rarely, green algae can also be found on land, largely on rocks and trees, with some appearing on the surface of snow. They are common in areas where light is abundant, such as shallow water and tide pools, and less common in the ocean than brown and red algae, but they can be found in freshwater areas.

Invasive Species

Some members of chlorophyta are invasive species. Cladophora glomerata bloomed in Lake Erie in the 1960s because of phosphate pollution. The rotting algae washed up on beaches and produced an odor so foul that it discouraged the public from enjoying the lakes. It became so offensive in sight and smell that it was confused for raw sewage.

Two other species, Codium (also known as dead man's fingers) and Caulerpa, threaten native plant life in coastal California, Australia, the Atlantic Coast, and the Mediterranean Sea. One invasive species, Caulerpa taxifolia, has been introduced into nonnative environments because of its popularity in aquariums.

Green Algae as Animal and Human Food and Medicine

Like other algae, green algae serve as an important food source for herbivorous marine life, such as fish, crustaceans, and gastropods, including sea snails. Humans use green algae as food, too. and it has long been part of the cuisine of Japan. There are more than 30 species of edible seaweed, which is naturally rich in minerals such as calcium, copper, iodine, iron, magnesium, manganese, molybdenum, phosphorous, potassium, selenium, vanadium, and zinc. Edible types of green algae include sea lettuce, sea palm, and sea grapes.

The pigment beta carotene, found in green algae, is used as a food coloring. Carotene also has been shown to be very effective in preventing some cancers, including lung cancer.

Researchers announced in January 2009 that green algae could play a role in reducing carbon dioxide from the atmosphere. As sea ice melts, iron is introduced to the ocean. This fuels the growth of algae, which can absorb carbon dioxide and trap it near the ocean floor. With more glaciers melting, this could reduce the ​effects of global warming. Other factors, however, can reduce this benefit; if the algae are eaten, the carbon can be released back into the environment.​​​​

Fast Facts

Here are some quick facts about green algae:

  • Green algae are also referred to as Chlorophyta and, sometimes, seaweed.
  • They convert sunlight to starch that is stored as a food reserve.
  • Green algae's color comes from having chlorophyll.
  • Green algae's habitat ranges from the ocean to freshwater and sometimes to land.
  • They can be invasive, with some species fouling beaches.
  • Green algae are food for sea animals and humans.
  • Green algae are used in cancer treatment.
  • They could help reduce carbon dioxide in the atmosphere.