I have the habit of reusing old potting soil when I fail my sowings.
So this may be a vegetable, but it could also be a weed.
It has started growing in my Citrus digitata pot, and I suspect it could be Amaranth-related... But it grows so fast compared to the Amaranth-related plants I grow that I find it fishy.
Would anyone know what it is. It's more than 4 feet high.