Equisetum (Latin, meaning horsetail) is a distinctive plant whose geologic time range is Eocene to Recent. It is native to North America, but it has spread to other continents (e.g., South America and is considered an invasive plant in New Zealand). There are about 15 species today, and they inhabit salt flats, banks of streams, and moist low parts of forests. They cannot live in water.
The higher classification of Equisetum is in a state of flux. It is closely allied to ferns based on how they both reproduce via spores and not by seeds. But Equisetum differs: Equisetum is stiff not soft, it does not have true leaves, it bears its spores in a capsule at the top of the plant rather than underneath leaves.
Above is a close-up of Equisetum showing the structures that contain the spores at the top of the plant.
Equisetum is the only living genus of joint-stem trees, which range back to Late Paleozoic time (Devonian Period), and had slender, unbranching, and longitudinally ribbed stems with a thick core of pith and rings of small leaves at each transverse joint. These trees were most abundant in sands and muds that accumulated along levees and floodplains of rivers but were uncommon in permanently wet swamps. During the Carboniferous interval, joint-stem trees were especially common.
Equisetum, also called “horsetail rush” or “water rush bamboo,” grows rapidly and can reach heights of up to 8 feet (2.5 m). Except for its relatively small size, modern-day Equisetum is very similar to the Late Paleozoic forms. Once a Equisetum plant gets established, it spreads via its rhizomes and can quickly colonize a substantial area if left unchecked. It is best to contain the plant with barriers.
Most species of Equisetum are referred to as “scouring rushes.” They have stems that are rough and abrasive due to the presence of silica deposits in the outer layer of the stem. They were used for cleaning (scouring) pots and pans in colonial days and are still used by many modern-day campers.
Another name for Equisetum is “snake grass.” The main reason is probably because it resembles a snake, with its tube-like body. In my experience, another reason is because when you walk through a stand of it, there is a harsh grating sound (because of the silica in the stems) that can sound like the rattle sound made by a rattlesnake!
Nurseries sell Equisetum for modest prices. It is a hardy plant that has a distinctive decorative look to it. The images below are of a stand of cultivated Equisetum hyemale that I found growing in small plot of land adjacent to a pool of water in a patio of a commercial building. These plants which have leafless stems standing erect 2 to 5 feet tall, with rigid dark-evergreen hollow jointed nodes with a blackish rim around them.
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