Spring-beauty (Claytonia virginica) 2010-4-3 Arkansas - this photo is not upside down, the flowers are growing out of a wall!

-usually pink, but can be so pale as to appear almost white
https://www.minnesotawildflowers.info/flower/virginia-spring-beauty
-another Spring Beauty is Carolina Spring Beauty (Claytonia caroliniana) but its leaves are shorter, more oval, and is an uncommon plant