I have the same issue with a Silver Maple tree's roots. I planted ferns around them and it looks very nice. How about hosta? My loriope works well under the shade also. Some other suggestions I have are lily of the valley or vinca vine.

Hmm.. Not so fond of Hostas, but the lilly of the valley is a pretty good idea even though they are not native and my in-laws have so we can take.

Paul

What about Lamium? It's a varigated ground cover that will spread and in the spring you will have spikes of yellow (or pink)flowers. Here is N.C. it seems to grown well.
Lynn

What kind of tree is it. Some of the woodland asters would do well along with the normal spring bulbs from say hepatica, dutchman's breeches etc. Of course what will grow there depends on the tree. I have tree peonies under an apple, oak, and black willow. All but the one's under the willow are doing well. They probably would be larger in another area but they are healthy.