Horsetails (Equisetum)

This group gathers Ferns and Fern Allies subcategory members belonging to the genus Equisetum, the horsetails, the sole surviving genus of an ancient lineage of vascular plants that was far more diverse and, in several extinct relatives, far larger during the Carboniferous period, when some tree-sized relatives formed a substantial part of the swampy forests that later became coal deposits. Recognizable by hollow, jointed, ridged stems, often with whorls of thin, needle-like branches radiating from each joint, and stem tissue reinforced with silica deposits that made horsetails a traditional natural material for scouring pots and polishing metal and wood before manufactured abrasives became widely available. Horsetails reproduce through spores released from a distinctive cone-like structure at the tip of certain stems, and several species spread aggressively through an extensive underground rhizome system that makes an established colony notoriously difficult to eradicate once it takes hold.