At the other extreme with regard to pollination mechanisms, some species of Thalictrum, meadow rue, are wind pollinated and have very small sepals and/or petals or none at all. In T. revolutum, the flowers are imperfect and the plants are dioecious. In this photo, a male plant in on the right while a female plant is on the left.
Photo by K. R. Robertson in Caldwell County, North Carolina.