I need to identify this plant that has spread through out a shady woodland...

The unidentified plant in your woodland bed is most likely an aggressive, native plant, Geum canadense, commonly known as White Avens. The confirmation of its identification will come in the next week or so when small white flowers appear at the junction of the three leaves. The plant is not poisonous. It is difficult to pull up, but usually requires control in order to keep it from spreading into unwanted areas.