That looks like a type of euphorbia called "snow-on-the-mountain". It's an annual in our zone. I haven't grown it, but have read that the sap can be highly irritating so be careful taking cuttings.

Thanks Motria!

:) Di

That's what it is peachy. It's great in cut arrangements and it will self seed everywhere if you let it. I used it in my daughter's wedding bouquets and i did have a reaction to the sap, but nothing serious.
mary