Equisetum hyemale var. affine

Native

Moist. Roadsides, woodlands, riverbanks, streambanks, lakeshores, and other moist or wet places.

8″ to 60″

This is an erect, evergreen, unbranched perennial that rises from rhizomes. It can be 8″ to 60″ tall, though in Minnesota it is usually 24″ to 48″ tall. It often forms dense colonies.

The stems are erect, ⅛″ to ½″ in diameter, dark green, and hollow. They are normally unbranched, but may develop one or a few branches after injury, or in the second year. They have 14 to 50 fine, vertical ridges with silica deposits making them rough to the touch. They are evergreen, lasting more than one year. The central cavity is at least ¾ 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 most of their length, and appressed against the stem, forming a collar-like sheath around the nodes. The main sheaths are tan, grayish, or white, with a black band at both the base and the tip. They are wider than long, 3 ⁄16″ to ⅜″ long, ⅛″ to ¾″ wide, and appear squarish. At the tip of the sheath are 14 to 50 free, 3 ⁄16″ long or less lobes appearing as tiny, black teeth. The teeth are jointed and may fall off at the joint at maturity, leaving just a dark rim on the sheath, but they often persist.

A solitary, spore-bearing cone is borne at the end of each fertile stem. The cone is ⅜″ to 1″ long, 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.

Smooth scouring rush (Equisetum laevigatum) is a shorter plant, only reaching 12″ to 36″ tall. The stems are lighter green, smooth to the touch, and annual. The sheaths are light green and have a black band at the tip only, sometimes also the lowest ones with a black band at the base or black throughout. The teeth on the sheath fall off promptly at maturity. The cones are inconspicuously apiculate.

Variegated scouring rush (Equisetum variegatum var. variegatum), is a much shorter plant, only 4″ to 18″ tall. The stems are much thinner, 1 ⁄32″ to 3 ⁄32″ in diameter. The sheaths are green with a black band at the tip, and slightly flared outwards at the tip. There are 5 to 12 vertical ridges on the stem and the same number of teeth on the sheath. The teeth have conspicuous white margins. They are not jointed. The cone is shorter, ⅜″ long or less. It is found only in the upper third of the state.

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 also 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”.