Complex sentence: They are very diverse and contain a variety of subdivisions, as well as yet-unclassified isolates, mainly because some genera are very difficult to classify because of a highly niche-dependent phenotype.
Split into simpler sentences: They are very diverse and contain a variety of subdivisions as well as yet-unclassified isolates. This is mainly because some genera are very difficult to classify because of a highly niche-dependent phenotype.