There are many instances where a population smoothly intergrades between two extremes that, in the absence of intermediate forms, would unquestionably be considered distinct varieties or even species. Such populations present great difficulties in classification. It is hard to decide if they represent two distinct taxa with hybrids in the middle, or alternatively represent a single taxon that simply has extremes of variation. The problem, she thickens, because those two possibilities may be mere mental constructs with no reality to them. The correct interpretation of such an intergrade may depend on the history of the populations, which is unknown. Examples: IIRC, an old forester once told me that Abies lasiocarpa in the west smoothly intergrades across Canada with another, eastern, species that is quite distinct. No one knows with any certainty which scenario the overall population represents - is it two species with a hybrid swarm or is it one species with wide variation, perhaps in the process of splitting into two species? Another example is Cyclmaen coum coum and its supposedly distinctive subspecies C. c. caucasicum. Extensive field work sponsored by the Cyclamen Society has shown that there is a continuous variation between the two extremes, to the point that there are lots of intermediates impossible to classify as one or the other. Sometimes you have to wonder if Mother Nature takes offense at human attempts to pigeonhole her creations and deliberately sets up these taxonomic pitfalls... -- Rodger Whitlock Victoria, British Columbia, Canada Maritime Zone 8, a cool Mediterranean climate on beautiful Vancouver Island