Pictured here is an example of Oenothera triloba, the Stemless Evening Primrose. It belongs to the Evening Primrose Family, Onagraceae. This species makes beautiful yellow flowers up to 3 inches in diameter. Notice the leaves at the bottom center of this photo, they are broad and irregularly lobed. This is a character that makes this species easy to tell from other yellow Primroses in the field.
In the second image, you can see a fully open flower in the background left of center. Notice the sepals underneath the flower are fully reflected. This is another characteristic of this species that is useful for field identification. In the foreground, another flower has just started to open. Its sepals have separated but haven’t reflected.
Stemless Evening Primroses are open from late afternoon, through the night and closes mid-morning of the next day. The cloudy day when these photos were taken gave me extra time to catch these flowers doing their thing.