The Equisetum species is commonly known as horsetails and scouring rushes. The name come from the Latin words “equus” meaning horse, and “seta” meaning bristle, animal hair.
Equisetum is referred to as a living fossil. This is because it is the only surviving genus of Equisetopsida. This class of plant dominated the plant kingdom, and was more diverse, in the Paleozoic forests. These plants were able, during this earlier time, to grow up to 30 meters high. Today these plants range from the E. Scripoides at 12.9 centimeters tall, to the giant horsetails, E. giganteum and E. myriochaetum, which reach eight meters or taller.
Equisetum are vascular plants which reproduce by spores that come from their cones.
Equisetum species are perennials. The plants themselves are made up of upright aerial stems that grow from an underground rhizome system which is quite extensive. The aerial stems have one main axis for their growth. This is similar to what is found in gymnosperms and angiosperms. The leaves appear in whorls and are reduced and fused into a shape like a sheath at the stem joints. The stem ridges and the number of leaves are usually equal in number.
Equisetum stems are erect and hollow. They appear to be jointed, and have a ridged surface which contains deposits of silica. The stems grow at regular spacing from the massive rhizome. This causes them to form colonies oftentimes. The fertile stems and the sterile ones may look similar but the fertile stems appear first. When the fertile stems appear they will have a cone at the tip. The environment may vary the height and the amount of branching that may occur. If there is branching, it will only be at the nodes.
The cones, which appear at the tip of the fertile stems, are made up of whorls of hexagonal spores. These spores are small and green, each one has four structures that are known as elaters. These elaters help with spore dispersal when the cone has split open longitudinally. Some of the cones are not branched and others are non-photosynthetic and appear in early-spring.
Equisetum can be identified, one from another by whether there is branching or not, the number of leaves and their habitat.
This plant can be found everywhere in the world except Antarctica. They may either be herbaceous and die back in the winter or they may be evergreen.
Even though many prefer wet sandy soil, there are some which are semi-awuatic and others that grow in wet, clay.