Actually what has happened in the last few hundred years to D. Leichhardtii in OZ is actually a perfect example of adaptive radiation and genetic bottlenecking. Simply put, while the plant started out genetically indentical and self-seeds, over the centuries selective pressures have weeded out some genes from showing up. To explain, The pruinosa sub-species is essentually a dwarf version with more tomentose leaves. Over the time that the weed has been growing, natural forces such as lack of water and the harsh austrailian sun have killed off the seedlings and plants who were the least adapted. That's why the species still remains relatively unchanged in the Northern part, there's little acting on the organisms to select for any traits so "if it ain't broke, don't fix it". The dwarf subspecies, with its furry leaf covering is better able to protect againsn't dessication and UV. As for your analogy about carrots, I agree with you that the line is very very blurry...sometimes even genetic screening can't tell much of a difference between populations. Just look at any oak species from hear to the midwest, a huge precentage of them are at least in some way a hybrid. So what we are witnessing is evolution in action. Also, I just thought I should mention that very recently botanist finally discovered how plants which self pollinate like mustard and datura don't just inbreed themselves into oblivion. Apperently the offspring keep a spare set of genes from the parent plant around somewhere in there own cytoplasm that can "patch" any missing proteins or otherwise fatal mutations that come from contant inbreeding. I personally think that's just another sign of how much more advanced plant life is on this planet comparied to animals and man, and it also shows that the rules for genetics aren't set in stone yet.
Peace,
Nate

Informative! Do you have any sources for that bit about self-pollinating plants keeping a spare set of genes around? I would be very much interested in looking into that. Also, do you know if those same plants produce new genetic sets every time a bit of the backup set is used, or is the spare genetic sequence reproduced in an identical fashion?

Getting off topic for a moment, gardengrove_ac, I recall that you were generous enough to offer some Datura stramonium seed to me, but I have not heard back from you, regarding that matter, nor have I received any seeds. That's just fine, seeing as I haven't sent anything out either, but I would like to know if you are still interested in a trade.