Equisetum arvense L.
Equisetum arvense L. var. alpestre Wahlenb.
Equisetum arvense L. var. boreale (Bong.) Rupr.
Equisetum arvense L. var. campestre Wahlenb.
Equisetum arvense L. var. riparium Farw.
Equisetum calderi B. Boivin
Horsetails are among the oldest members of the fern family, dating back 300 million years to the Carboniferous Period. They are largely unchanged from when dinosaurs ruled the earth. Field horsetails have high levels of silicon (10%!), and were once used to polish pewter and wood. Horsetails are found almost everywhere in North America. Like all horsetails, they are fond of damp soil, but these also grow in fields, woods, waste places, and glades. They prefer light shade, but will grow in full sunlight as well.
Plants: Fertile stems, which are tipped by strobili, spore-bearing conelike structures, are pale brown (nonphotosynthetic), erect, and unbranched. They are 6-12" (15-30 cm) tall. They appear early in the season and are gone by May. Sterile stems (no “cone”) are green, 6-24" (15-60 cm) tall, ¹/₁₆-³/₁₆" (3-5 mm) in diameter, with 4-14 ridges. They appear after the fertile stems have come and gone. They are highly variable, usually heavily branched in a series of upward-pointing whorls, usually erect, sometimes prostrate. Branches are thin, shaped like a plus sign in cross-section. Stem and branch surfaces feel rough, due to the presence of silica—tiny glasslike spheres absorbed from the soil and deposited in the plant.
See Equisetum for a comparison chart.
Leaves: Tiny, dark brown sharp-tipped leaves surround the stem at nodes. They do not perform photosynthesis.
Fruits: Conelike structures that are neither cones nor fruits appear atop the fertile stems. They are 1-1½" (2.5-3.8 cm) long, with blunt tips.
Medical: Native Americans and early settlers made a diuretic tea from this plant.
Edibility: The buds are eaten in Japan, but other portions of the plant and all other species of Equisetum are toxic. Unless you are a grizzly bear, in which case field horsetails make up about 3-5% of your diet. Black bears also consume it, despite its low nutritive value.
Equisetum arvense at Skye Flora
Equisetum arvense on Wikipedia
Equisetum arvense on the USDA Forest Service's Fire Effects Information Database
Equisetum arvense on Plants for a Future, a resource and information centre for edible and otherwise useful plants
Equisetum arvense on Calflora
Equisetum arvense on eFloras
Cobb, Boughton, Farnsworth, Elizabeth & Lowe, Cheryl, Peterson Field Guides: A Field Guide to Ferns and Their Related Families of Northwestern and Central North America, Houghton Mifflin Company, 2005, p. 340
Equisetum arvense description by Thomas H. Kent, last updated 3 Dec 2020.