Which species are assigned to a genus is somewhat arbitrary. Although all species within a genus are supposed to be "similar" there are no objective criteria for grouping species into genera. There is much debate among zoologists whether large, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance, the lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets. 
Due to limited resources, FDA is unable to perform independent clinical studies, and the agency lacks the regulatory authority to require the generic industry to conduct such studies. FDA will, however, continue to investigate these reports to ensure that it has all the facts about these possible treatment failures and will make recommendations to health care professionals and the public if the need arises. Currently, to better understand what may cause problems with certain formulations if, in fact, they are linked to specific generic products, FDA is encouraging the generic industry to investigate whether, and under what circumstances, such problems occur.