According to my late father and erstwhile gardener, there is no such thing as a weed.
"A weed is a flower in the wrong place", he said.
While I agreed, letting agents sometimes don't and expect us to keep our garden free of anything that anyone might describe as a 'weed'.
This afternoon, I noticed what appeared to be a weed growing out of the gravel that runs down the side of our garage.
I pulled it.
Definitely no weed. It's a parsnip.
How did it get there? Your guess is as good as mine.