Evening Primrose Oenothera biennis blossoms remain open through the night. For that reason, Germans call them night candles. There are several blossoms to each head of this 3-5 foot tall biennial. The blossoms are about 2 inches across and have an x-shaped stigma. This one can often be seen along roadsides or fence rows. The entire plant is edible and was a staple among several Native American tribes. Oil made from its seeds is used as a health supplement.