Freshwater Algae of North America
   Class Zygnematophyceae C.Hoek, D.G.Mann & H.M. Jahns (1995), nom. inval. - conjugating green algae see Class Zygnematophyceae Round ex Guiry (2013)
     Order Desmidiales - placoderm desmids
       Family Desmidiaceae Kützing ex Ralfs (1845)
         Genus Phymatodocis Nordst. (1877)
           Phymatodocis alternans Nordst.