Cutleaf Eveningprimrose (Oenothera laciniata)

Flowering plant as seen in May and June.  Stems hairy, reclining, branched from base.  Leaves alternate on lower stem to opposite on upper stem, oblong to lanceolate, irregularly lobed to deeply incised, flower single, sessile in leaf axis with 4 yellow petals and 4 distinct down-pointing sepals.