Certified GKH Gardening Expert
There are a couple of plants referred to as snow on the mountain and I've included information on both. If you have the euphorbia, it is an annual that reseeds and the new plants next year will probably look normal.
The one also called Bishop's Weed is hardy to zone 3 and is a groundcover. You can pinch out the green ones, which will take over if you don't.