Burrs grow on Burdock. (I think it's an introduced species, here on the coast of British Columbia, Canada.) Burdock wasn't common in my neighbourhood when I was a little girl; I first became acquainted with burrs on a family visit to relatives in the UK. On departing thence, Mom remembered me saying farewell to memorable features of the British landscape, like sheep and stone walls. Forgetting the word "burr" I called out, "Bye-bye, colds."

I don't know the name of the long black seeds like grass seeds that work their way through your socks with backward-pointed bristles and jab you with their sharp tips. I haven't seen them in a while.

You could use "stickers" as a generic word for hitchhiking seeds.