Giant horsetails are usually living species of horsetail that grow to very large sizes, more than 1.5 metres (5 ft). 
The following species are commonly known as "giant horsetails":
In addition, any giant member of the Equisetopsida (horsetails and their prehistoric relatives) is liable to be called "giant horsetail" even though they are not true horsetails. Most often, the term "giant horsetail" in this somewhat inaccurate sense refers to Calamitaceae in Paleozoic contexts; in the Mesozoic, the term usually refers to the "Equisetites" assemblage.
The oldest known fossil of giant horsetail dates from Miocene epoch and is found in Ñirihuau Formation in Patagonia.
References.
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 Index of plants with the same common nameThis page is an index of articles on plant species (or higher taxonomic groups) with the same common name (vernacular name). 