any of a genus (Oenothera) of plants of the evening-primrose family, with yellow, pink, or white flowers, many of which open in the evening
adjective
designating a family (Onagraceae, order Myrtales) of dicotyledonous plants found chiefly in temperate America, including the fuchsia, sundrops, and willow herbs
See evening primrose in American Heritage Dictionary 4
noun
Any of various North American plants of the genus Oenothera, characteristically having four-petaled yellow flowers that open in the evening. Also called sundrops.