Euphorbia prostrata Aiton
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Much like no. 31 [Euphorbia maculata L.], but with the lvs more variable in outline, chiefly less than 1 cm, with the styles bifid to the base or nearly so, and with the sharply quadrangular seeds marked with 3 or 4 conspicuous transverse ridges, is rarely adventive (from s. U.S.) and probably not persistent in our range. (E. chamaesyce, misapplied)