Thanks a lot, Almas John. That’s two mysteries solved. I don’t regard them as weeds. I regard them as wildflowers. One man’s trash is another man’s treasure.
I also often come across a strange plant that has tiny fern-like leaves which are so sensitive that if you touch any of the leaves, then all of the tiny leaves on that stem close up and stay closed for about 2 or 3 minutes. Here’s a picture of a whole patch of the “sensitive plant”:
And here’s a close up of one of them:
Does this plant have a name, other than just calling it the “sensitive plant”?