This post is by Jocie Brooks, leader of the Botany Group, adapted from her email to members of the group on May 12.
Horsetail and scouring rush are distinctive plants, with bamboo-like jointed stems and a strange rough-to-touch texture. They are also ancient, living fossils that transport us back to prehistoric times when they flourished 300 million years ago in the swampy landscape of the Carboniferous period. Artists’ re-creations of that period often depict tree-sized horsetails, the Calamites, with dinosaurs roaming through them. These are fascinating plants, true survivors of the trials of time.
Horsetails are in the Phylum Sphenophyta, of which there is only one living Genus today, Equisetum, which means “horse bristle.” There are 15 species of horsetail in the world and they are among the oldest surviving vascular plants on earth. Horsetails grow from perennial rhizomes that can grow a metre deep. In the spring, annual shoots arise that are hollow, ribbed and jointed. Whorled branches fan out from the joints and inconspicuous leaves form a sheath with pointed teeth. The whole plant has a coarse texture due to the presence of silica dioxide. Scouring rush differs in that it has no branches, and the shoots are perennial.
The three most common species in our area are:
- Giant horsetail (Equisetum telmateia) this is the largest horsetail in our area, common in wet places such as swamps, marshes, ditches and stream sides. It is not found east of the coast mountains. The species name telmateia means “of muddy water or swamps.”
- Common horsetail (Equisetum arvense)is a smaller species that is circumpolar. It grows in a variety of habitats, and can tolerate sun exposure and poor soils, often colonizing roadsides and disturbed places. It is notoriously hard to remove from the garden!
- Scouring rush (Equisetum hyemale) has no branches, and has darker, blue-green stems. All of the stems look alike and are evergreen.
How do horsetails reproduce?
Many species of horsetail produce green vegetative shoots that are sterile, as well as ghostly, colourless fertile shoots with a cone-like structure, or strobilus at the tip. The strobilus is packed with small, plate-like sporangiophores that are ringed with spore-producing sporangia. A spring-like elater is coiled around each spore, and when conditions are right, the spores are shot into the air. Spores grow into the beginnings of a new plant, the gametophyte, which is either male or bisexual. Male gametophytes (like mosses and ferns) have sperm with flagella that require water to swim to female plants. The fertilized plant, now called the sporophyte begins to grow and eventually detaches from the gametophyte and develops to maturity.
First Nations/Traditional use
Fertile shoots of horsetail were traditionally harvested by many coastal groups. The new spring shoots were eaten fresh or boiled after the tough outer fibers were removed. Saanich people thought the shoots were good for the blood. Squamish people used to drink water from the hollow stem segments of giant horsetail.
Horsetail, especially the green shoots, can be extremely toxic to livestock and humans, causing weakness and trembling and in some cases coma and death. It is recommended that the green shoots are never eaten, and fertile shoots should only be consumed “in small quantities and with extreme caution.”
Scouring rush was used as an abrasive, a bit like sandpaper, for polishing a variety of wooden implements. In colonial times it was used as a pot-scrubber.
The tallest horsetail in the world is the Mexican giant horsetail (Equisetum myriochaetum) which grows in wet, fertile soils in Mexico and Central/South America and reaches heights of 15 feet.
Horsetail is a very tough plant, that can tolerate disturbance and poor soils with metals and/or salinity. Its ability to form colonies and spread by deep rhizomes and tubers is also key to its success. After the eruption of Mt. St. Helens, horsetail was the first vascular plant to grow.
Plants of Coastal BC (Pojar & MacKinnon), Illustrated Flora of British Columbia (Douglas, Meidinger & Pojar), Biology of Plants (Raven, Evert, Eichhorn), Food Plants of Coastal First Peoples (Nancy Turner), Encyclopedia of Life (eol.org)