This looks like a young filbert or other nut tree most likely popping up because squirrels plant the seeds in your planters or anyplace there is soft soil. I suggest you put your hand inside a plastic bag and then pull it out as soon as you see it appear. A volunteer plant like this looks like it will become a woody tree or shrub and overtake and shade your other plants. In my experience if you don't uproot saplings while they are young the root system will spread so fast that pulling them out of the ground will become difficult and you'll be stuck digging them out and disturbing all the nearby vegetation. In a more open space if you have lots of room you can let one grow if you are curious. Sometimes it is fun to see what nature has planted for you. Keep growing, Marianne Binetti