Annals of Botany Hemicellulose evolution in monilophytes (Research in Context) The Equisetopsida emerged in the Upper Devonian (>370 mya), and Equisetum (horsetails) may be the oldest surviving vascular plant genus. Horsetails and the Poales are the only plants possessing the hemicellulose (1... botanyoneJuly 9, 2012