Bidens cernuus is a member of the Aster family, and each large "flower" is actually a head of many small flowers. There are many species in this family, of a wide variety of appearances. Be advised that identification based on photo matching is not reliable and you should turn to the keys in Michigan Flora or the web site for KEYS TO THE ASTERACEAE OF WISCONSIN.

The leaves of Bidens cernuus are "perfoliate", meaning that each opposite pair appears to be joined at the base with the stem passing through the middle. There are other perfoliate plants such as Eupatorium perfoliatum, but the flowers in that species are white and of very different design. The "seeds" (actually fruits) of Bidens cernuus have retrorsely barbed margins and awns at the tips, serving to readily attach them to the fur or feathers of passing animals, or to the clothing of people. The size of a plant can vary wildly, from an inch or so with a single flower, to 5 feet or more tall and bushy with many flowers.

Bidens cernuus is an annual species of wet, muddy edges, often appearing after water levels have fallen, exposing previously flooded sites. They are then quickly outcompeted on the site if water levels remain low, or the seeds will fail to germinate in successive years if water levels rise enough to flood the site. The result is that you may find large and vigorous populations in one year and return in subsequent years to find few or no plants on the same site.