Equisetum arvense, the field horsetail or common horsetail, is an herbaceous perennial plant in the Equisetopsida (the horsetails), 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.

The erect sterile stems are 10–90 cm tall jointed segments around 2–5 cm long. As a child i used to love pulling the segments apart and marvelled how they fitted together again.

Equisetum is a "living fossil", the only living genus of the entire subclass Equisetidae, which for over 100 million years was much more diverse and dominated the understory of late Paleozoic forests.

Courtesy of: en.wikipedia.org/wiki/Equisetum

It is very troublesome in a garden, so don't even think of putting a container of it into your garden pond!