Tall Tumblemustard - Sisymbrium altissimum

 This four-petaled flower in the Mustard Family (Brassicaceae) is attractive right now, but unfortunately it's non-native to North America, where it is widespread. This is tall tumblemustard (Sisymbrium altissimum). Over the summer it dries out and eventually strong winds can snap the plant down and blow it around, further spreading seeds. Of historical interest, it is thought that early railroads helped distribute this species.

It can grow 3-5 feet high, and leaves are deeply divided at the base.

For more info on tall tumblemustard, click here.