|evening-primrose (Oenothera spp.)||
evening-primrose (Oenothera spp.; EVENING-PRIMROSE FAMILY [Onagraceae]) A dozen species of relatively stout annual, biennial, or perennial herbs. Showy yellow flowers (1½-2") are borne in the axils of the leaf like bracts, have a long slender calyx tube, 4 flaring yellow petals, and a prominent cross-shaped stigma. Evening primrose flowers open at twilight, sundrops (same genus) open at mid day. Common on road edges and dry waste places. Flowers, then produces distinctive rod-shaped fruits throughout the summer. 
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