Responding to some of the bits in this thread:
-By most credible accounts, "green crack" (formerly "green cush") is a select pheno of a cross between an old SSSC Skunk #1 and a CA-acclimated indica. Which indica? I don't know, and I'm not sure anyone does. . .that info is lost in time. Supposedly the name "green crack" came as a tongue-in-cheek comment about the strain from Snoop Dogg himself.
-Green crack is not the same thing as "Space Queen". Its also not the same as KC brains mango, though it does have a somewhat similar mango-like scent.
-For obvious reasons, many of the dispensaries that sell this don't like their medical cannabis being likened to ghetto rock cocaine, and so this strain does go by other names, such as "Green Kush/Cush", "Green Candy", etc.
-The strain is hugely popular because its just combines an outstanding mix of great scent/flavor, high potency, sativa-like high quality, good yield, and fast flowering time. Very few strains give you that whole package, but this one does. This one is also easy to clone, which helped spread it around.
-If you can even find any, Riot seeds "Green crack" S1-selfed seeds are really pricey. A new company called Sick-Meds seeds has just this past August released its own feminized S1 Green Crack seeds, and they're available at a few places now, including Cannazon at a much more reasonable price. These are so new that there are no reviews on them yet, but I'm quite sure that will change in the next few months since beans have been spread out to various testers for review.
I just don't get this clone only thing... What's stopping someone from just buying these clones at a dispensary and taking them past flower to produce seeds? Or am I missing something?
First of all, not every line will make male flowers if taken late into flowering; typically only strong sativa-dominant strains will do that. In this case, I kind of doubt that this one will, since both parents (Skunk and CA indica) are probably fairly hermie resistant. This particular strain probably wouldn't have become as popular as it is, if it were hermie-prone.
But in general, nothing is preventing anyone from selfing a Green Crack clone either the way you describe, or using chemical agents like colloidal silver, to create self-pollenized S1 seeds if they like. As mentioned, riot seeds has already put out commercially available seeds like this, and Sickmeds seeds currently has them at a much more reasonable price. So not only "can" it be done, it HAS been done, and you can even buy the seeds if you like.
My question is really, how close to the original clone are these selfed seeds going to be?
You might think that fertilizing a female plant with its own pollen "should" create a genetically identical plant. But in fact, that's a common misconception that's only true if the parent plant is true-breeding.
If the parent plant is a hybrid (which Green Crack, by all accounts, is), then crossing it with itself is tantamount to an ordinary F1 cross between two hybrid parents.
When you cross two different hybrid plants, you expect to yield a wide variety of phenotypes in the F2 generation. In this case, the S1 seeds are effectively the product of an F1 cross, and they should therefore be like F2 seeds. Some of these F2 plants are likely to be similar to the mother. But certainly not all of them, nor even necessarily most of them, and some selection will probably be necessary to find one that is close. At that point you'd still have to clone THAT plant to maintain it, sort of defeating the purpose of the whole exercise!
Even if you were to backcross one of these selfed S1 plants with the original mother to try and "purify" the genetics, again, you're still crossing two hybrids, and will run into a wide variety of phenotypes, only some fraction of which will be like the original.
And this explains to a large part, why there even are such thing as "clone only" strains. If anyone could just self a clone and make seeds from it, then there would be absolutely nothing special about "clone only" strains, and all of them could be/would be readily available in seed form.
The best way to create authentic Green crack seeds would be to obtain cuts of the original parents and cross them again to recreate the line, though for multiple reasons this isn't possible either.