7 Major Types of Algae

Algae in a Lake
This image shows algae in a lake. Like plants and bacteria, algae are autotrophs. They are capable of self nourishing or generating their own food, typically from sunlight. Credit: Moritz Haisch/EyeEm/Getty Images

Pond scum, seaweed, and giant kelp are all examples of algae. Algae are protists with plant-like characteristics, that are typically found in aquatic environments. Like plants, algae are eukaryotic organisms that contain chloroplasts and are capable of photosynthesis. Like animals, some algae possess flagellacentrioles, and are capable of feeding on organic material in their habitat. Algae range in size from a single cell to very large multicellular species, and they can live in various environments including salt water, freshwater, wet soil, or on moist rocks. The large algae are generally referred to as simple aquatic plants. Unlike angiosperms and higher plants, algae lack vascular tissue and do not possess roots, stems, leaves, or flowers. As primary producers, algae are the foundation of the food chain in aquatic environments. They are a food source for many marine organisms including brine shrimp and krill, which in turn serve as the nutrition basis for other marine animals. 

Algae can reproduce sexually, asexually or by a combination of both processes through alternation of generations. The types which reproduce asexually divide naturally (in the case of single-celled organisms) or release spores which may be motile or non-motile. Algae that reproduce sexually are generally induced to produce gametes when certain environmental stimuli – including temperature, salinity, and nutrients – become unfavorable. These algae species will produce a fertilized egg or zygote to create a new organism or a dormant zygospore that activates with favorable environmental stimuli.

Algae can be categorized into seven major types, each with distinct sizes, functions, and color. The different divisions include:

  • Euglenophyta (Euglenoids)
  • Chrysophyta (Golden-brown algae and Diatoms)
  • Pyrrophyta (Fire algae)
  • Chlorophyta (Green algae)
  • Rhodophyta (Red algae)
  • Paeophyta (Brown algae)
  • Xanthophyta (Yellow-green algae)


Euglena gracilis / Algae. Roland Birke/Photolibrary/Getty Images

Euglena are fresh and salt water protists. Like plant cells, some euglenoids are autotrophic. They contain chloroplasts and are capable of photosynthesis. They lack a cell wall, but instead are covered by a protein-rich layer called the pellicle. Like animal cells, other euglenoids are heterotrophic and feed on carbon-rich material found in the water and other unicellular organisms. Some euglenoids can survive for some time in darkness with suitable organic material. Characteristics of photosynthetic euglenoids include an eyespot, flagella, and organelles (nucleus, chloroplasts, and vacuole).

Due to their photosynthetic capabilities, Euglena were classified along with algae in the phylum Euglenophyta. Scientists now believe that these organisms have acquired this ability due to endosymbiotic relationships with photosynthetic green algae. As such, some scientists contend that Euglena should not be classified as algae and be classified in the phylum Euglenozoa.


Diatoms. Malcolm Park/Oxford Scientific/Getty Images

Golden-brown algae and diatoms are the most abundant types of unicellular algae, accounting for around 100,000 different species. Both are found in fresh and salt water environments. Diatoms are much more common than golden-brown algae and consist of many types of plankton found in the ocean. Instead of a cell wall, diatoms are encased by a silica shell, known as a frustule, that varies in shape and structure depending on the species. Golden-brown algae, though fewer in number, rival the productivity of diatoms in the ocean. They are usually known as nanoplankton, with cells only 50 micrometers in diameter.

Pyrrophyta (Fire Algae)

Dinoflagellates pyrocystis (Fire algae). Oxford Scientific/Oxford Scientific/Getty Images

Fire algae are unicellular algae commonly found in oceans and in some fresh water sources that use flagella for motion. They are separated into two classes: dinoflagellates and cryptomonads. Dinoflagellates can cause a phenomenon known as a red tide, in which the ocean appears red due to their large abundance. Like some fungi, some species of Pyrrophyta are bioluminescent. During the night, they cause the ocean to appear to be aflame. Dinoflagellates are also poisonous in that they produce a neurotoxin that can disrupt proper muscle function in humans and other organisms. Cryptomonads are similar to dinoflagellates and may also produce harmful algal blooms, which cause the water to have a red or dark brown appearance.

Chlorophyta (Green Algae)

Green Algae
These are Netrium desmid, an order of unicellular green algae that grow in long, filamentous colonies. They are mostly found in freshwater, but they can also grow in saltwater and even snow. They have a characteristically symmetrical structure, and a homogeneous cell wall. Marek Mis/Science Photo Library/Getty Images

Green algae mostly abide in freshwater environments, although a few species can be found in the ocean. Like fire algae, green algae also have cell walls made of cellulose, and some species have one or two flagella. Green algae contain chloroplasts and undergo photosynthesis. There are thousands of unicellular and multicellular species of these algae. Multicellular species usually group in colonies ranging in size from four cells to several thousand cells. For reproduction, some species produce non-motile aplanospores that rely on water currents for transport, while others produce zoospores with one flagellum for swimming to a more favorable environment. Types of green algae include sea lettuce, horsehair algae, and dead man's fingers.

Rhodophyta (Red Algae)

Red Algae
This is a light micrograph of part of the finely branched thallus of the red algae Plumaria elegans. So-called for its elegant appearance, here individual cells in the filamentous branches of this algae are visible. PASIEKA/Science Photo Library/Getty Images

Red algae are commonly found in tropical marine locations. Unlike other algae, these eukaryotic cells lack flagella and centrioles. Red algae grow on solid surfaces including tropical reefs or attached to other algae. Their cell walls consist of cellulose and many different types of carbohydrates. These algae reproduce asexually by monospores (walled, spherical cells without flagella) that are carried by water currents until germination. Red algae also reproduce sexually and undergo alternation of generations. Red algae form a number of different seaweed types.

Paeophyta (Brown Algae)

Giant Kelp
Giant kelp (Macrocystis pyrifera) is a type of brown algae that can be found in underwater kelp forests. Credit: Mirko Zanni/WaterFrame/Getty Images

Brown algae are among the largest species of algae, consisting of varieties of seaweed and kelp found in marine environments. These species have differentiated tissues, including an anchoring organ, air pockets for buoyancy, a stalk, photosynthetic organs, and reproductive tissues that produce spores and gametes. The life cycle of these protists involves alternation of generations. Some examples of brown algae include sargassum weed, rockweed, and giant kelp, which can reach up to 100 meters in length.

Xanthophyta (Yellow-Green Algae)

Yellow-green Algae
This is a light micrograph of Ophiocytium sp., a freshwater yellow-green alga. Gerd Guenther/Science Photo Library/Getty Images

Yellow-green algae are the least prolific species of algae, with only 450 to 650 species. They are unicellular organisms with cell walls made of cellulose and silica, and they contain one or two flagella for motion. Their chloroplasts lacks a certain pigment, which causes them to appear lighter in color. They usually form in small colonies of only a few cells. Yellow-green algae typically live in freshwater, but can be found in salt water and wet soil environments.

Key Takeaways

  • Algae are protists with characteristics that resemble those of plants. They are most commonly found in aquatic environments. 
  • There are seven major types of algae, each with distinct characteristics. 
  • Euglenophyta (Euglenoids) are fresh and salt water protists. Some euglenoids are autotrophic while others are heterotrophic.
  • Chrysophyta (Golden-brown algae and Diatoms) are the most abundant types of single-celled algae (approximately 100,000 different species).
  • Pyrrophyta (Fire algae) are single-celled algae. They are found in both the oceans and in fresh water. They use flagella to move around.
  • Chlorophyta (Green algae) typically live in freshwater. Green algae have cell walls made of cellulose and are photosynthetic.
  • Rhodophyta (Red algae) are mostly found in tropical marine environments. These eukaryotic cells do not have flagella and centrioles, unlike other types of algae.
  • Paeophyta (Brown algae) are among the largest species. Examples include both seaweed and kelp.
  • Xanthophyta (Yellow-green algae) are the least common species of algae. They are single-celled and both cellulose and silica make up their cell walls.
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Bailey, Regina. "7 Major Types of Algae." ThoughtCo, Sep. 3, 2021, thoughtco.com/major-types-of-algae-373409. Bailey, Regina. (2021, September 3). 7 Major Types of Algae. Retrieved from https://www.thoughtco.com/major-types-of-algae-373409 Bailey, Regina. "7 Major Types of Algae." ThoughtCo. https://www.thoughtco.com/major-types-of-algae-373409 (accessed May 29, 2023).