Equisetum hyemale affine / Equisetum praealtum
E. hyemale ssp./var. affine = E. praealtum*,
North America, Mexico, Central America in Guatemala.
E. hyemale ssp./var. hyemale = E. hyemale,
Europe and Asia to northwestern China in Xinjiang.
The two subspecies differ morphologically in height, stem colour
and width and numbers of ridges on the sheath teeth.
*E. praealtum may be treated as a separate species. [Christenhusz et al. 2019]
However, if one prefers to keep this taxon as a subspecies, the correct name
would be E. hyemale subsp. affine.