The common mare's tail, Hippuris vulgaris (from greek: ἵππος — horse and οὐρά — tail), is a common aquatic plant of Eurasia and North America ranging from Greenland to the Tibetan Plateau to Arizona. It prefers non-acidic waters. The species is also sometimes called horsetail, a name which is better reserved to the horsetails of genus Equisetum. These are unrelated to H. vulgaris, although there is some resemblance in appearance.