SSAR split Sistrurus tergeminus from Sistrurus catenatus taking
Desert Massasauga (Sistrurus catenatus ssp. edwardsii)
and Western Massasauga (Sistrurus catenatus ssp. tergeminus) with it. https://www.inaturalist.org/taxon_changes/18657

This leaves Eastern massasauga (Sistrurus catenatus ssp. catenatus) all alone so I'm collapsing it into Sistrurus catenatus