Greg,
Those are some very good points, and of course you are right: even from a single collection site there can be great variability within the populations. Even the "type" collection is only a part of the picture. Without pouring over herbarium sheets there is little hope of understanding what "typical" implies.
Christian, this problem exactly highlights the difficulty you are having in trying to match your (or others) plants of D. natalensis to an "exact fit". I remain unconvinced that this is possible regarding the South African species. I expressed my own frustrations in this regard to Dr. Schlauer in trying to ascertain what a typical specimen of D. natalensis would be. He told me the populations in Madagascar are likely to be as pure an example as can be had.
I just want to add that the use of "aff." is a very good descriptive tool. I have so many variations of D. dielsiana that I have taken to labeling most of them in this fashion. With every variation I grow comes a greater certainty that no private growers can claim to have a "true" form. Even those who review extensive sheets of collected material are often hard pressed in this regard: Key descriptions are based on extensive review of the field material, and this sort of experience collectors will never be able to access, not if we were to grow 300 plants! Use they keys as a guide, certainly but remember that the variability factor will always enter the equation.
I recently asked Robert how one determines the most significant focus on these species: is it the styles, stipules or seeds? Is there some sort of point value assigned to these qualities the total of which adds up to a reasonably certain determination? His reply was that he too struggles to understand this same issue.
"Variation in D. dielsiana, as with many other rosulate species of sundews shows how little we still know and understand species' limits and the relative weight of various factors. Clearly cytology data is not sufficient to explain most of this variation, and it now appears that even genetic sequencing may not be the great clarifier either given it is more than simple presence or absence of a gene that determines genotype, for it is how genes interact that morphology is also determined. Detailed field studies are needed of plants in the wild throughout their range to get an understanding and context of the variation we see in listed clones on innumerable seed lists. That many names attached to these seeds are often erroneous makes it even more challenging to understand what is going on when basing any study on cultivated material."
" I feel that the taxonomic weight of some characters has been overplayed and that they vary greatly in accordance with only minor changes to the genotype (but have yet to test this hypothesis)". (Robert Gibson Pers. Comm.)"
A "sticky" problem to be sure!