I grew a bunch of seeds about three years ago now that I bought online, and then when I went back to look the following year, they didn't have any more. This is the result of the first years seeding:
I save the seeds every year now, and I've sold some online. I figured I should test them to see if they were viable (they look just like dust - how can they possibly grow?) and I ended up with this:
They each had twins...