A major nomenclatoral work for liverworts, begun in 1962 under Dr C.E.B. Bonner, and continued after his death in 1976 by Helene Bischler and Patricia Geissler, the current editors.
The first nine volumes were compiled under the editorship of Dr Bonner. Some of these are completely out of print, but most have been reprinted in recent years by J.Cramer Verlag.
The series is ongoing, with 12 volumes completed thus far.