Equisetum variegatum var. variegatum

Native

Wet. Thickets, bogs.

4″ to 18″

This is an erect, 4″ to 18″ tall, evergreen, unbranched perennial that rises from rhizomes.

The stems are erect, slender, 1 ⁄32″ to 3 ⁄32″ in diameter, green, unbranched, and hollow. They have 5 to 12 vertical ridges with silica deposits making them rough to the touch. They are evergreen, lasting more than one year. The central cavity is ¼ to ⅓ the diameter of the stem. The portion of the stem between the nodes is up to several inches near the bottom, becoming progressively shorter as they ascend the stem.

The leaves are reduced in size, fused together for part of their length, and appressed against the stem, forming a collar-like sheath around the nodes. The sheaths are 1 ⁄16″ to 3 ⁄16″ long, poorly marked at the base, and slightly flared outwards at the tip. They are green with a black band at the tip only. At the tip of the sheath are 5 to 12 free lobes appearing as tiny teeth. The teeth have a black, 1 ⁄16″ wide, 2-ridged stripe in the center and conspicuous white transluscent margins. The teeth are not jointed and usually persist.

A solitary, spore-bearing cone is borne at the end of each fertile stem. The cone is small, ⅜″ long or less, circular in cross-section, and elliptic in long section. It ends with a small but conspicuous, abrupt, flexible point at the tip (apiculate). Infertile stems are similar to fertile stems but lack the terminal cone. The cone falls off after releasing spores.

Scouring rush horsetail (E. hymale var. affine) is a much taller plant, usually reaching 24″ to 48″ tall. The stems are much thicker, ⅛″ to ½″ in diameter. The sheaths appear squarish, are tan, grayish, or white, and have a black band at both the base and the tip. There are 14 to 50 vertical ridges on the stem and the same number of teeth on the sheath. The teeth are jointed. The cone is longer, ⅜″ to 1″ long.

Smooth scouring rush (E. laevigatum) is a taller plant, reaching 12″ to 36″ tall. The stems are thicker, ⅛″ to 5 ⁄16″ in diameter, lighter green, smooth to the touch, and annual. There are usually 16 to 30 vertical ridges on the stem and the same number of teeth on the sheath. The teeth are jointed and fall off promptly at maturity. The cone is longer, ⅜″ to 1″ long, rounded at the tip, and often inconspicuously apiculate.

Taxonomy
There are 15 species of Equisetum, which is the only living genus in the family Equisetaceae, which is the only family in the order Equisetales, which is the only order in the class Equisetopsida. The history of Equisetum has been traced 300 million years to the Cretaceous period, and possibly to the Triassic period. That could make Equisetum the oldest living genus of vascular plants.

The genus Equisetum is divided into two subgenera, Equisetum and Hippochaete. scouring rush horsetail is one of the eight species in the subgenus Hippochaete. Four of those eight species are found in North America. All four of those occur in Minnesota.

In this subgenus, the stems are unbranched or have few irregular branches. They are coated with an abrasive silica, and were used for scrubbing cooking pots. This, along with their rush-like appearance, gave rise to the common name “scouring rush”.