Flowering Spurge

One or more bright green stems grow erect to 3 ft. A whorl of smooth, bright green leaves surrounds the stem at the point where 3-7 flowering stalks branch off. Minute flowers surrounded by 5 white, round, petal-like bracts attached to rim of a cup, all in a few- to much-branched, open cluster atop each stem; sap milky. Each flowering stalk branches again above another whorl of smaller leaves. Flowering stalks are topped by small, white flowers in a large, loose, long-lasting, flat-topped clusters.
Leaves appear to be somewhat variable. Compare to this specimen: http://www.projectnoah.org/spottings/57706021