Most of us encounter algae in the form of seaweeds, green filaments or films in ponds or lakes or even coatings on trees or rocks in moist environments. Algae is a general term used to describe an extraordinarily diverse group of organisms from solitary cells to complex multicellular forms reaching several metres in length which all produce oxygen by photosynthesis. They all contain chlorophyll although the green colour of the pigment is often masked by accessory pigments.
This group includes both eukaryotes (possessing internal membranes and therefore organelles such as chloroplasts and nuclei) and the prokaryotes (lacking membrane-bound organelles),consequently algae belong to various taxonomic super groups (kingdoms) Plantae, Protozoa, Chromista and Eubacteria.