Equisetum giganteum

Description

It is one of the largest horsetails, growing 2–5 metres (6.6–16.4 ft) tall, exceeded only by the closely allied Equisetum myriochaetum (up to 8 metres (26 ft) relying on surrounding plants' support. One form or variety has reached a height of 36 feet (eleven meters) in Venezuela, and a height of 39 feet (twelve meters) in the Pantanal region of Brazil. The stems are the stoutest of any horsetail, 1–2 cm diameter (up to 3.5 cm (1.33 inches) in diameter in some populations), and bear numerous whorls of very slender branches; these branches are not further branched, but some terminate in spore cones. Unlike some other horsetails, it does not have separate photosynthetic sterile and non-photosynthetic spore-bearing stems.

Populations from northern Chile with very stout stems up to 3.5 cm diameter have sometimes been treated as a separate species Equisetum xylochaetum, but this is not widely regarded as distinct. The thickest specimen to be reported by a trained botanist is 1.57 inches (four centimeters) by Dr. Thomas Schoepke on the Lluta River near Arica, Chile circa 1999–2000.