been made. In 2004, using DNA from Peridiscus, it was shown that Elatinaceae and Malpighiaceae are indeed sister families and that Peridiscaceae belong to Saxifragales. Medusandra and Soyauxia, meanwhile, were listed in APG II in an appendix entitled "TAXA OF UNCERTAIN POSITION". DNA from Soyauxia was eventually obtained, and in 2007, it was shown that Soyauxia is most closely related to Peridiscus and, presumably, Whittonia. Since this result has a good morphological basis, Soyauxia was duly transferred to Peridiscaceae. This study also found strong statistical support for the inclusion of Peridiscaceae in Saxifragales, but no strong support for any particular position within that order. In 2008, in a study employing a large amount of chloroplast DNA data, as well as some mitochondrial and nuclear DNA, it was shown that Peridiscaceae is sister to the rest of Saxifragales. It had been suspected that Medusandra might belong somewhere in Malpighiales, but a phylogeny of that order, generated in 2009, placed Medusandra in Saxifragales. The authors had included Medusandra and a few other members of Saxifragales in their outgroup, finding strong support for a clade of [Medusandra + (Soyauxia + Peridiscus)]. When the APG III system was published in October 2009, Peridiscaceae was expanded to include Medusandra and Soyauxia. John Brenan, 57 years before, had been prescient in his perception of a relationship between Medusandra and Soyauxia. Phylogeny The phylogeny is diagrammed as a phylogenetic tree below. The relationships shown are from Wurdack and Davis (2009) except for the position of Whittonia, for which no DNA sequences are known. Peridiscus and Whittonia are undoubtedly sister taxa due to their many shared morphological characters. References Bibliography Websites Peridiscaceae At: Angiosperm Phylogeny Website At: Missoure Botanical Garden Website CRC World Dictionary of Plant Names: M-Q At: Hooker's Icones Plantarum Peridiscaceae in L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. Saxifragales families