As I was weeding, I noticed several of the pictured plants sprouting up between my dahlia plants. I pulled up all but one, and realized I had no idea what they were. I posted in the dahlia forum, and was told that it wasn't a dahlia as it has alternating leaves. I didn't even notice that, and now I'm stumped.

This plant is about 3-4 inches tall, and sprouted within the last week. I don't know if it helps, but in the surrounding area I have daylilies, dahlias, boxwoods, holly bush, oak leaf hydrangea, and muscari. I have not seen this plant pop up before, so I'm thinking it found it's way there recently. Any ideas? Thanks!!!

I am thinking about just letting it grow just to see what it is, but is that a good idea or no?