While chlorella is a well known
nutritional supplement in Japan and many countries in South East Asia, it is
still relatively unknown in Europe, where there is a degree of confusion over
the different types of chlorella that are available.  In fact,
this confusion has been shared by consumers and scientists alike in the
past.  This is due to the similarity in the different strains
of chlorella which has led to problems classifying them. 
Classification is normally done on the basis of cell size, cell shape, biochemical
and physiological characteristics.  However, as these factors aren’t
consistent across members of the same chlorella species, it is often
difficult to know exactly which species of chlorella a sample
is.  There are in fact over 100 types of chlorella, so the common perception
that chlorella is only available asChlorella Vulgaris
and Chlorella Pyrenoidosa is a gross over-simplification.  In
fact, some chlorella researchers have even
removed Chlorella Pyrenoidosa as a classification, arguing that this
particular strain of chlorella is simply a collection of different
types of chlorella that have been misclassified
and subsequently classified as other non-chlorella species.