The Genus Equisetum:
Equisetum is a genus that remains from the Carboniferous (about 350-300 million years ago). Horsetails plants like equisetum were the dominant plant type.
The reduced leaves in Equisetum contain no chlorophyll, so photosynthesis is carried out by the stems and branches, if present. Horsetails are also called scouring rushes because the epidermal cells contain hard silica deposits, which made them useful for scouring pots and pans before the invention of steel wool scouring pads.
Source: www.northernontarioflora.ca