What is "equisetum arvense"

Paddock \Pad"dock\, n. [OE. padde toad, frog + -ock; akin to D. pad, padde, toad, Icel. & Sw. padda, Dan. padde.] (Zo["o]l.) A toad or frog.
--Wyclif. ``Loathed paddocks.''
--Spenser

Paddock pipe (Bot.), a hollow-stemmed plant of the genus Equisetum, especially Equisetum limosum and the fruiting stems of Equisetum arvense; -- called also padow pipe and toad pipe. See Equisetum.

Paddock stone. See Toadstone.

Paddock stool (Bot.),a toadstool.

Equisetum arvense, the field horsetail or common horsetail is a herbaceous perennial plant, 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. It is commonly confused with mare's tail, Hippuris vulgaris.