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 Peniaceae Haeckel (1894) [paraphyletic] 1 Genus Penium Bréb. ex Ralfs (1848)