in botany, a genus of the dioecia erneandria clasf. The calyx of both male and female consists of three segments; neither of them have any corolla; the stamens are from nine to twelve; the anthers are globular and didymous; the female has two styli; and the capsule has two cells, and one seed in each. There are four species, two of them natives of Britain, viz. the perennis, or dogs mercury; and the annua, or French mercury.