It’s safe to say there are hundreds, if not over 1,000 strains today, with many more under development. The ability of cannabis to adapt to new environments over many centuries, spread its genetics, and change its characteristics is remarkable.
Because if its ability to adapt, there are numerous cannabis strains with unique combinations of genetics. However, remember that just because a strain is named, does not mean it’s unique. Some strains may be an established genetic and the person growing it simply changes its name and starts selling it as a unique strain.
New strains are constantly being created through cross breeding, and some strains have never even been characterized. New genetic testing technologies and changes in state law (and hopefully federal and international law too!) will undoubtedly lead to the characterization of new strains and eventually determine how many truly exist.