Three species of Chlorella
Today botanists consider that three species constitute the Chlorella group:
Chlorella vulgaris, Chlorella lobophora and Chlorella sorokiniana (Krienitz et al., 2004).
Organic Chlorella eChlorial is exclusively composed of the species vulgaris.
Chlorella pyrenoidosa would be a mixture of species composed mostly of vulgaris.
Chlorella vulgaris and Chlorella pyrenoidosa?
According to the classification of taxa, “Chlorella pyrenoidosa” CHICK and Chlorella vulgaris BEIJERINCK are chlorophytes, called green algae.
The organisms called Chlorellaceae belong to the chlorophytes (green algae) to the group of Trebouxiophyceae. Chlorellaceae are divided into two related groups, the parachlorella group and the chlorella group, which includes Chlorella vulgaris (Krienitz et al., 2004). These are cocciated green algae with small, spherical green cells, which is why chlorella is often also referred to as a “green ball”. However, the most diverse algae in different groups have this appearance, which is called convergent morphology (comparable to the convergent morphology of many succulent euphorbia and cacti).
In summary, the classification and differentiation of Chlorella is difficult and remains a matter for specialists. They are species with most of the characteristics very similar and moreover can vary strongly (morphologically and physiologically). Of course, this complicates the determination and classification, with the consequence of erroneous classifications and duplications. More than 100 species of Chlorella have been described, most of which had to be revised.
To distinguish the different species from each other, different characteristics have been (and are) studied: e.g. ultrastructure of the cell wall, ultrastructure of the pyrenoids, chemical composition of the cell wall, serological cross-reactions, physiology, biochemistry, morphology and molecular biology. In 1992, among other things, various deposits of algal cultures named “C. pyrenoidosa” were examined, showing that the cultures named C. pyrenoidosa should be classified in very different species. Thus, for example, strains of C. vulgaris that had been deposited under the name “C. pyrenoidosa” could be identified.
A large part of the C. pyrenoidosa algal cultures actually belonged to the species C. sorokiniana and since then “C. fusca” is no longer classified in the genus Chlorella but in the closely related genus Scenedesmus (Kessler & Huss; 1992).
In other words: according to the most recent findings, the species “Chlorella pyrenoidosa” does not exist, but rather is an obsolete term that grouped together species and strains belonging to different algal groups.
At present, three species constitute the Chlorella group: C. vulgaris, C. lobophora and C. sorokiniana (Krienitz et al., 2004).
As of 1999, only these three species and C. kessleri were still included in the genus Chlorella (Huss et al., 1999). Chlorella vulgaris BEIJERINCK is the species that gives the name to the genus and is deposited as a so-called “type” species with official collections. It was isolated and described for the first time in 1889 in Delft (Netherlands) by Professor M.W. Beijerinck.