Defining "species" is dependent on what one intends to use the definition for. Look in many books in phylogenetics and you will see several formal definitions. Biologist use different ones of those several definitions depending on what direction their research is taking and what methodologies are available to them to use. This leads me to feel that there is probably no such thing as a "species" but rather many ways of viewing the biological world. Our discomfort with this, if any, is probably because our subconscious minds are still trying to fit everything into a pre-Darwinian frame of reference, which contained fixed, rigid species. Taxonomy is not the Platonic Ideal of biology but rather a heueristic tool for use in real life. For my own interests in biology, the AGP III system works just fine. More than that, it makes very good sense to a biochemist! Jim Shields At 07:42 PM 10/31/2012 +0100, Christian wrote: >What do you think about the AGP III system for flowering plants? >http://onlinelibrary.wiley.com/doi/10.1111/… >The approach, mainly molecular-based, has reorganized a few plant >famillies, earlier classified based on more classical parameters such as >those discussed here. > >It seems that defining what a species is difficult because the living world >will always come with a specific example conflicting with the definition - >therefore the amount of definitions existing for a species depending on the >approach. ************************************************* Jim Shields USDA Zone 5 P.O. Box 92 WWW: http://www.shieldsgardens.com/ Westfield, Indiana 46074, USA Lat. 40° 02.8' N, Long. 086° 06.6' W