The APG II system, of 2003 (unchanged from the APG system, of 1998), does recognize Cymodoceaceae and places it in the order Alismatales, in the clade monocots. The family includes five genera, totalling 16 species of marine plants occurring in tropical seas and oceans (so-called seagrasses).
According to the AP-Website it is doubtful if the family Ruppiaceae is distinct enough to be kept apart: the plants in the three families Cymodoceaceae, Posidoniaceae and Ruppiaceae form a monophyletic group.
Flora Malesiana Series I - Seed Plants. Volume 16. Caryophyllaceae, Cunoniaceae, Potamogetonaceae, Zosteraceae, Cymodoceaceae
Jan 01, 2004; K. Larsen, H. C. Fortune Hopkins, R. Hoogland, C. den Hartog & G. Wiegleb (authors). H. P. Nooteboom (General editor). Flora...
Short-term spatial variations in the beds of Ruppia maritima (ruppiaceae) and Halodule wrightii (cymodoceaceae) at Grand Bay National Estuarine Research Reserve, Mississippi, USA.
Apr 01, 2008; ABSTRACT Studies have reported extensive losses of Submersed Aquatic Vegetation (SAV) habitat along the Mississippi coast, but...