Just want to make things even more complicated. While subspecies are a "can of worms" since there is no recognized standard for there seperation (they can all interbreed), even species designations are sometimes controversial. The biological species concept is based on the inability to interbreed to produce fertile offspring, but some well recognized species can do just that. For example, upland cotton and pima cotton are well recognized seperate species that, when bred together, can produce fertile offspring. Thus, plant breeders routinely move genes back and forth between these species through crossing. I am a bit of a purist, and think that a species designation should be reserved for populations that cannot exchange genes through conventional breeding, but others disagree. Subspecies in one taxonic aria can be very closely related while very different populations in another taxonomic area are given no such status. Pretty boring stuff huh?