Marestail (also mare's tail and mare's-tail) may refer to:
Plants Conyza canadensis, an annual weed also known as horseweed and Canadian fleabane Equisetum, a fern ally also known as horsetail and pipeweed Hippuris, a genus of aquatic flowering plants, including: Hippuris vulgaris, the common mare's-tail
Other Mare's tail, a type of cirrus cloud formation
See also Grey Mare's Tail (disambiguation)