What is this plant?

This started growing in my garden in a shaded spot next to a spirea. Any idea what it is? It looks lettuce like.

Check and see if it has milky sap, and whether the leaves are fuzzy or not. That would help to narrow it down.

Can you scratch some of the dirt away at the base , without killing it, and see what the root looks like?

Ok, the leaves are fuzzy but there is no milkiness
I can clear away some of the soil tomorrow and take a picture. Is there anything I should look for?
Thanks!

It would be easy to identify with flowers. However, my first instinct from the leaf photos is that it could be something from the Mustard family:

http://www.wildflowers-and-weeds.com/Plant_Families/Brassicaceae.htm

Try crushing and smelling the leaf. All mustard species have a unique smell, but there is an underlying pattern of mustardness that can be highly useful for identifying most members of the family. If you have other Mustard family plants in the yard, try smelling them, and comparing the smell to your plant in question.

I hope this helps!

Sincerely,

Thomas J. Elpel
http://www.hopspress.com/Books/Botany_in_a_Day.htm

Looks like comfrey.