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)
     1 Order Zygnematales [paraphyletic] - filamentous conjugates and saccoderm desmids
     1.n Order Desmidiales - placoderm desmids