1. Aquatic: Both fresh (Oedogonium, Spirogyra) and marine (Ulva, Sargassum, Marcocystis). Marine are larger.

2. Terrestrial: Nostoc, Oscillatoria, Fritschiella tuberosa

3. Unusual

1. Endophytic: Found inside other plant. Eg: Nostoc punctaeforme in thallus of  Anthoceros, Anabena inside leaf of Azolla
2. Endozoic: Found within body of other animal. Eg: Zoochlorella and Zooxanthella inside hydra 
3. Epiphytic: Algae attached to the body of other plants, including algae. Eg: Scytonema- bark of tree, Bulbochaete- Cladophora
4. Epizoic: Found attached to body of animals. Eg: Cladophora- on snail's shell, Stigeocolonium- on gills of fish, Characium- attached to mosquito
5. Cryophytic: Found in low temp. Eg: Chlamydomonas yellowstonensis- cause green snow
6. Cryptophytic: Found below soil. Eg: Chara (stone wort)
7. Thermophytes: Algae which can resist high temperature. Eg: Occilatoria brevis, Gleocapsa, Haplosiphon
8. Lithophytic: Found on rock. Eg: Revularia, Scytonema
9. Halophytic: Found on salty area. Eg: Chlamydomonas ehrenbergii
10. Parasitic: Eg: Cephaleurous veriscence- red rust of tea
11. Benthic: Eg: Algae found at the bottom of water. Eg: Chara(stone wart)
12. Epiphyllophytes: Aerial epiphytes that grow in leaves of tree. Eg: Phycopetis
13. Epiphloephytes: Aerial epiphytes that grow on bark of the tree. Eg: Scytonema
14. Edapophytes: Found in damp soil. Eg: Oscilatoria (blue-green algae)