According to their habitat algae are classified into seven groups.
These are aquatic, free floating or completely submerged algae.
Terestial algae are called Edaphic algae. They live upon or inside the surface of earth. Edaphic algae are classified into two types,
Saprophytes E.g. Mesotaemium, Botryduium
Crypyophytes E.g. Nostoc, Anabaena
These are aerial forms of algae. They are found upon trunks of trees, walls, fencing wire, rocks and animals. Aerial algae are classified into four types. They are,
Epiphyllophytes E.g. Trentepohlia
Epizoophytes E.g. Chaetophorales
Lithophytes E.g. Sctonema, Vaucheria, Nostoc
Algae living on ice and snow are called cryophytes or cryophytic algae.
Eg. Chlamydomonas, Ankistrodesmus and Mesotaenium.
Symbionts or Endophytes:
Algae growing in symbiotic association with other plants are called symbionts. There are three types. They are,
· Symbiotic with fungi E.g. Chroococcus, Nostoc, Chlorella and palmella
· Lives inside the pteridophyte Azolla. Eg. Anabaena azollae.
· Found in the corolloid roots of Cycas. Eg. Anabaena cicadae.
Algae living inside the body of animals are called Endozoic algae.
· Inside fresh water sponges
· Inside Hydra
Algae live as parasites on other plants. Eg.Cephaleuros virescens.