Bidens leptocephala

Bidens leptocephala, the fewflower beggarticks, is a North American species of flowering plant in the daisy family. It is native to the southwestern United States (Arizona, New Mexico, western Texas) and northern Mexico (Chihuahua, Sonora, Baja California, Baja California Sur).
"Bidens leptocephala" is an annual herb up to 50 cm (20 inches) tall. Flower heads are sometimes borne one at a time, sometimes in groups of 2 or 3, each head yellow or white with disc florets and sometimes with ray florets. The species usually grows on streambanks.