Chlorella is a member of eukaryotic organism (true nucleus plant), which has been on earth since the pre-Cambrian period over 2 billion yeas ago. It is not a sexually reproducible plant but unicellular, freshwater green alga, which divides itself so rapidly into four times in every 20 to 24 hours. (From the latest gene analysis of Chlorella, it turned out that it was 540 million years ago that Chlorella and Chlamydomonas diverged from a common ancestor.)

Chlorella is so small with 3 to 8 micrometers in diameter that appeared before the public only in the end of 19 centuries. At that time, chlorella was named after "chlor" which means green in Greek and "ella" which means a small thing in Latin.

For a long period of time, chlorella has survived every convulsion of nature because of its tough outer cell wall protecting its genetic integrity and its rapid reproductive ability. Oxygen now exists on earth was generated from sunshine, water and carbonic acid gas that algae like chlorella produced with their highly photosynthetic capacity. At the same time, they produced various fundamental nutrients that many organism generated in later period needs to support life.

With its capacity for photosynthesis which is several tens of times higher than that of other plants, chlorella produces an amazingly large amount of protein that is about 38 times that of soy beans, and about 55 times that of rice. Another characteristic is its copious yet well-balanced amounts of nine essential amino acids, as well as vitamins and minerals.

There are many species of chlorella, but Chlorella pyrenoidosa (SUN CHLORELLA stain) was found to be especially rich in nutrients. In Japan it was studied as a possible "dream food" which saves food shortage after defeat in the war, and later studies have brought many people nowadays to use it as a health food.