Equisetum telmateia, the great horsetail or northern giant horsetail, is a species of Equisetum (puzzlegrass) with an unusual distribution, with one subspecies native to Europe, western Asia and northwest Africa, and a second subspecies native to western North America.[1] The North American subspecies is often simply but ambiguously called "giant horsetail", but that name may just as well refer to the Latin American Equisetum giganteum and Equisetum myriochaetum.
It is an herbaceous perennial plant, with separate green photosynthetic sterile stems, and pale yellowish non-photosynthetic spore-bearing fertile stems. The sterile stems, produced in late spring and dying down in late autumn, are 30cm–150cmcm (10inches–60inchescm) (rarely to 240cm (90inches)) tall (the tallest species of horsetail outside of tropical regions) and 1cm (00inches) diameter, heavily branched, with whorls of 14–40 branches, these up to 20cm (10inches) long, 1– diameter and unbranched, emerging from the axils of a ring of bracts. The fertile stems are produced in early spring before the sterile shoots, growing to 15cm–45cmcm (06inches–18inchescm) tall with an apical spore-bearing strobilus 4cm–10cmcm (02inches–00inchescm) long and 1cm–2cmcm (00inches–01inchescm) broad, and no side branches. The spores disperse in mid spring, with the fertile stems dying immediately after spore release. It also spreads by means of rhizomes that have been observed to penetrate 4m (13feet) into wet clay soil, spreading laterally in multiple layers.[2] Occasionally plants produce stems that are both fertile and photosynthetic.[1] [3]
There are two subspecies:[4]
It is found in damp shady places, spring fens and seepage lines, usually in open woodlands, commonly forming large clonal colonies.[1] [3]