There are many species of horsetail in our region, but for Botany (BIOL223), you just need to know the genus Equisetum. All the species in the genus (and family too) have many characteristics in common, so though you may be unsure of the exact species, you can be quite sure that it is a horsetail you’re looking at.
Today, all horsetails are herbs and don’t grow particularly tall (in our area, the tallest are probably around 2 m in a really favourable site, but most are much shorter). However, fossil evidence shows that hundreds of millions of years ago, tree-sized species of this lineage used to exist. Much of the coal deposits around the world are formed from the accumulated biomass of these ancient horsetail forests.
Horsetails grow best in moist or wet areas, but some species (e.g. Equisetum arvense) do quite well even in drier places such as gardens where they can be quite aggressive weeds.
Horsetails often form dense stands. They have an underground stem (a rhizome) that is criss-crossing just under the surface of the soil, from there, stems emerge to form a dense stand. If you handle the plant you’ll notice that it feels quite rough to the touch. Horsetails (and most grasses) accumulate silicates (glass!) in their tissues. This makes them unpalatable to herbivores, but occasionally useful to people. Particularly rough species of horsetails have been collected and used as abrasives, in e.g. wood- or metal-work, in cultures around the world. Photo credit: Hitomi KimuraMany horsetail species produce two types of shoots/stems with different functions: one type (reproductive shoot) is pale and it’s only job is to make spores for sexual reproduction, the other type (the vegetative shoot) is green and does the job of photosynthesis. In this photo, we’re looking at a green vegetative shoot. Some species of horsetail lack the horizontal branches, and just look like ribbed green stalks coming out of the ground. The stem is segmented and can be easily pulled apart into separate segments – because of this feature, a former Botany student called it the “Lego plant”. Photo credit: Hitomi Kimura This is an example of fertile/reproductive shoots of horsetail. These pale shoots show up in the spring. The “cones” at the tip carry the spore producing structures. The youngest and most tender of these pale shoots have traditional uses as a spring vegetable in our region. Please note that the green portions of the plant are considered poisonous. Photo credit: Douglas Fraser A segment of a vegetative horsetail stem. Horsetail morphology is very unusual: The brownish-tan toothed sheath on the central stem are highly modified, fused leaves. The green ‘spokes’ that emanate from the central stem are not leaves, but branches. In horsetails, green stems have taken on the job of photosynthesis, and the leaves have all but disappeared. Note the distinctive ribs on the central stem. This is a characteristic of all horsetails. Photo credit: Douglas Fraser
