Algae is an informal term for a large, diverse group of photosynthetic organisms which range from unicellular genera such as chlorella and the diatoms to multicellular forms such as giant kelp may grow up to 50m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types which are found in land plants and the most largest and complex marine algae is seaweeds . Algae exhibit a wide range of reproductive strategies from simple asexual cell division to complex forms sexual reproduction.
Microalgae are typically found in freshwater and marine systems. The biodiversity is enormous that about 200,000 ~800,000 species. Over 15,000 novel compounds originating from algal biomass.
Macroalgae is usually called seaweeds and refers to several species of macroscopic, multicellular and marine algae. The term includes some types of red, brown and green algae and be classified by use as food, medicine, fertilizer, filtration and other industries.