Mine had to have come from a direct seed source. I never had them
until about 5 years ago. At that time I was raising some exotic
finches and other birds. I'd moved the cages to a row run shed
behind the house, and the following season, I was seeing strange
weeds in the goat fields next door. Some of the hard seed that are
in small birdseed mix are thistles, rape, and a whole host of other
things I can't remember (canary grass, etc.) This would have either
been something the birds didn't eat, or the percentage of clean
seed mixes that are actually wild seeds.
Before I joined BDNOW, I was always cussing my nettles in the
early spring. Now I've learned that, in all things, there is balance,
even the lowly nettle.