Plants medium-sized to large, rarely small, green or yellowish green.
Branch leaves smaller than stem leaves.
However, because some small phenotypes of Sanionia may also have smooth or almost smooth leaves, the last character should be used with caution. Features separating Sanionia from Hamatocaulis , Loeskypnum , Scorpidium , or Warnstorfia are pointed out in the notes after the family description. A widespread genus with four species in the Holarctic region, all occurring in North America. The genus occurs also in the southern hemisphere. Sanionia is still in need of taxonomic revisions in many geographical areas, and the distributions of the species outside North America, N and W Europe are partly incompletely known.