Blooming now in Pennsylvania, the evening primrose fully opens at twilight. Similar species called sundrops are open during the day.
Evening primroses are hardy and widespread, in fields and along roadsides. Dianne Machesney found this one at Scotia Barrens.
(photo by Dianne Machesney)
p.s. Monday August 13: It's cloudy and gray this morning. Evening primroses are open in Schenley Park.