A perennial grass that is dimorphic, having a fertile stem in the spring which dies back and is replaced by a sterile stem in early summer. The fertile stem is brownish in color, shorter and unbranched. The sterile stem is green with whorls of needle-like leaves and jointed stems. Also known as scouring rush, shavegrass, bottlebrush or pewter wort. Our horsetail consists of the sterile, ærial parts harvested in the summer months between June and August.