My theory on concrete and plants:
- Thats a LOT of dirt and material without any competition for the roots.
- Water/moisture is in the cracks/holes/etc.... so it helps the plant with constant moisture control.
- Some plants know how to take care of rocks and paths are just big rocks.
- Random selection as this one seed is extremely good at surviving.
Just some thoughts. I have a fruit tree that LOVES it next to concrete. I get fruit every year from that thing.