( HORSETAIL )
a "living fossil", as it is the only living genus of the entire class
Equisetopsida, which for over one hundred million years was much more
diverse and dominated the understory of late Paleozoic forests.
Some Equisetopsida were large trees reaching to 30 meters tall; the genus Calamites of family Calamitaceae for example is abundant in coal deposits from the Carboniferous period.