Annual mercury
Mercurialis annua

This is an annual herb growing 10 to 30 centimeters tall with oppositely arranged oval leaves each a few centimeters long. The male flowers are borne in spikelike clusters sprouting from leaf axils, and female flowers grow in clusters of 2 or 3. The fruit is a bristly capsule 2 or 3 millimeters wide containing shiny, pitted seeds.