Unusual White Flower

i looked in my peterson's wildflower guide book and cannot find the id of this flower. i remember it having prickles and thistle like leaves. it is on the edge of the woods and i will check tomorrow. if anyone knows its name, please let me know.

btw i have chigger bites from my forays into the wild blipping flowers. itch itch itch.

pinhani--istanbulda