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Published online by Cambridge University Press: 12 June 2017
A select few of our present-day weeds are descended from much grander primeval forms. Field horsetail (Equisetum arvense L. ♯ EQUAR) and related species are “degenerate” herbaceous plants whose tree-sized ancestors dominated forests in the Carboniferous period about 300 million years ago. Indeed, early equisetums contributed significantly to the formation of coal beds (12).