Q. What is Revisions?
Revision accounts for only a section of a genus or for the elements as restricted to a continent or smaller geographical area. Some revisions are based solely on herbarium studies and make no attempt to review all previous work on the taxon or to take care of the interrelated sciences of taxonomy, genetics, ecology etc.
It should be noted that there are no modem bibliographies devoted to the subjects of monographs and revisions of the world. The bibliographies by Pritzel, Jackson, Rehder and Merrill and Walker list several thousand monographs and revisions.