Equisetum arvense, also known as the field horsetail or common horsetail, is a herbaceous perennial plant in the Equisetidae (horsetails) sub-class, native throughout the Arctic and temperate regions of the Northern Hemisphere. It has separate sterile non-reproductive and fertile spore-bearing stems growing from a perennial underground rhizomatous stem system. The fertile stems are produced in early spring and are non-photosynthetic, while the green sterile stems start to grow after the fertile stems have wilted and persist through the summer until the first autumn frosts. This fertile spore-bearing E. arvense stem was photographed in Keila, Estonia.Photograph credit: Ivar Leidus