Oenothera biennis L., commonly known as Evening Primrose as flowers open in the evening. Inflorescence is racemose (spike) and flowering continues for about 3 months. Circular floral nectary of translucent colour are present at the point of attachment of petals and hypanthium. Pollen are triporate, of variable sizes held together by viscin threads. Sepals colour change from green to yellowish green, act as indicator of anther dehiscene in the morning in closed conditions and anthesis in the evening. | Evening primrose (Oenothera biennis L.): Morphology and reproductive biology
