As in Equisetum giganteum, the hollow stem of Equisetum hyemale owes the mechanical
stability of the internodes to an outer ring of strengthening tissue (hypodermal sterome)
which provides stiffness and strength in the longitudinal direction. In contrast to hollow‐
stemmed grasses, the hypodermal sterome consists of living cells. The compound inner
tissue of the overwintering aerial stem of Equisetum hyemale includes a continuous inner
and outer endodermis layer of vital thick‐walled cells that have slightly lignified Casparian …