As Craig recognized, our mystery seeds last week were from a plant known as purpletop vervain, Verbena bonariensis.
Verbenas are common landscape plants in Arizona because they are heat and drought tolerant and give long-lasting blooms.
Purpletop verbain is sometimes misidentified as Brazilian verbena, Verbena brasiliensis. The flowers of the Brazilian verbena are quite different from the purpletop.
The flowers are so lovely on this plant. The photographs don't do them justice. We are glad the birds decided to "plant" it.
Have you ever had an interesting plant like this one show up in your yard? What was it?