That's what I was thinking, but every picture of milkweed I've seen show the leaves are opposing pairs, or the picture is not good enough to tell for sure. The leaves on this plant are not opposing pairs, but single leaves. Still wondering, hoping I can find a definitive picture to confirm.
Looks like one of the larger evening-primrose (Oenothera) to me. Does it start out with a rosette of leaves flat on the ground before it gets to the stage shown? If I'm right the stalk will continue to grow and be topped with a spike of yellow, 4-petaled flowers that open in the evening and close the next day.....