Wednesday, June 9, 2010

Historic Horsetail

What can we learn from a family of plants that is 400 million years old? After all, the ancient horsetail (Equisetum spp.) has hardly changed during its long history with dinosaurs, humans and bears. What do we really know about this common native plant?

Brown spore-bearing horsetail stem and green vegetative stem (c) John Ashley
Vegetative stem (left) and strobulus (right)

Equisetum (from the Latin equus "horse" + seta "bristle") is the only living descendant from a group of plants that once dominated the Paleozoic forests. The horsetail family was a successful group long before the rise and fall of dinosaurs. Some of their ancestors lived with early dragonflies that had 2.5 foot wingspans. These ancient horsetails were many of the plants that died and slowly compressed into the coal that we dig up and use today.

Modern day horsetails are smaller, 2" to 14" tall plants that often favor wet areas. There are at least seven species native to Montana.

Most of each horsetail plant lives deep in the ground. A large underground rhizome sprouts two different kinds of above-ground stems: brown and green. Pale brown spore-bearing stems ("strobulus") arise in spring, followed by the familiar green vegetative stems with their wispy whirled branches.

Below the visible stems, underground rhizomes grow more than six feet deep. (This is why pulling, plowing and burning have little or no effect.) At one-foot intervals, the rhizomes branch out sideways and grow food-storing tubers.

Most reproduction is by asexual sprouts from the rhizomes. Horsetails don't produce flowers. For sexual reproduction the horsetail grows brown, spore-bearing stems during May and June.

The spore-bearing strobulus is a pale brown cone because it lacks chlorophyll. The tiny spores start out as male and female gametes, but over time the female spores also grow male parts, resulting in male and bisexual gametes. The gametes are less than 0.016 inches tall, only a few cells thick, and short-lived. Male sperm must travel through water to reach an egg-bearing female part, so sexual reproduction is thought to be rare in horsetails.

As the brown cone stems start to shrivel, the familiar green stems begin to elongate. The whirls are actually slender branches, and the tiny leaves have been reduced to small brown scales around the stem.

Green whirled branches and brown leaf scales (c) John Ashley
Whirls of small, brown leaves and long green branches
As horsetail matures, abrasive silica crystals form in the stems and branches, and a new group of neighbors found this trait to be quite useful.


Long after the horsetail ancestors saw the giant dragonflies and dinosaurs come and go, humans appeared on the scene. Horsetail has a long history of medicinal and practical uses by humans. Written, herbal horsetail remedies date back to the ancient Greeks and Romans.

Native Americans also made wide use of horsetail for food and medicine. Crow and Flathead Indians used it as a diuretic, and the Blackfeet boiled it to make cough medicine for horses. Cree and Crow Indians used horsetail to relieve abdominal pains.

Natives and early settlers ate the young horsetail shoots raw or cooked, like asparagus. They also drank a diuretic tea brewed from horsetail, and made green dyes for lodges and clothing.

The rough silica crystals made dried horsetail a favorite tool for scouring and polishing. Settlers gathered bundles of horsetail and used them to scour floors and polish metal, especially pewter. Some Native Americans still use horsetail to polish ceremonial pipes, as well as bows and arrows. Indian children even made whistles from the hollow horsetail stems -- a use that was echoed by early Europeans.


Green horsetail shoots are 15% protein by dry weight. But eating too much horsetail can be poisonous to its namesake -- horses. While Captain Clark (of Lewis and Clark fame) noted that, "the horses are remarkably fond of it," horsetail can cause paralysis and death in horses. It is seldom eaten by other livestock, and deer and elk avoid it as well.

Bears, on the other hand, love the stuff.

Bears stay alive by eating their vegetables. The most important bear foods are forbs in spring (horsetail, clover, dandelions), ants in summer, and berries in the fall. For most bears, meat is just an occasional bonus. Plants and ants stave off starvation until the bears can fatten up on fall berries.

For Montana's grizzlies, forbs are important throughout the bears' active period. In spring, horsetail is the bears' favorite food across northwestern Montana. In summer, horsetail ranks 10th out of 32 food items eaten by grizzly bears in the southeastern corner we call Yellowstone.

Native horsetail growing in stream (c) John Ashley
Horsetail growing in water
 The menu is similar for black bears in Banff, north of Montana. In two studies, horsetail comprised 38% and 34% of spring black bear diets. During summer, horsetails were the second-most sought after food item, after ants.

Bear diet and habitat use both change with plant availability. Bears start at low elevation sites in spring and follow plant development to higher elevations in summer. In this way, bears eat horsetails that are in their immature, most nutritious stages, relatively higher in soluble nutrients and lower in fiber than mature plants.


Horsetail has survived many millions of years longer than humans. These plants managed to hang on during periods of mass extinction and global climate change. In the process, they grew their roots deep and helped their neighbors fend off illness and starvation. Can we learn any lessons from this ancient family?