Which species of Oenothera is this?

[Sinajuavi]

I planted a small packet of complimentary seeds whose identity is now lost to me, but they were "Evening Primrose". One original plant survived to go to seed, resulting in a little forest of plants, all of them reaching 7 feet and more in height, long branched stems from the base, with the expected yellow flowers but which open in the morning and are closed by afternoon. Morning Primrose I call it.

What is going on here?

 

[oneeye]

Can you post a photo because I want to see what you are talking about?