Weldenia canadida

A must have toughie.

This Mexican native has a rosette of broad, strapped leaves. The central, three-petalled, large, bright white flowers are borne over a long period in late spring and summer. Usually under snow in winter its an easy plant for those tough spots. It likes perfect drainage especially in winter and sun when in growth. I have it in the worst, sandiest parts of my garden and it thrives. Just leave it alone and watch it bulk up. (slowly) 

Potted specimen: sunoochi, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons