The phylogenetic position of Prionium (Juncaceae) within the order juncales based on morphological and rbcL sequence data

In this study we estimate the phylogenetic position of the South African genus Prionium within the order Juncales. Prionium is traditionally included within the family Juncaceae. However, trees based on rbcL sequence data have indicated that Juncaceae is paraphyletic because Prionium is not included within Juncaceae. Morphological and rbcL sequence data are analyzed separately and then in a combined data set to assess the phylogenetic position of Prionium. Each of these analyses supports a basal position of Prionium within Juncales. The monophyly of Juncaceae sensu lato is not corroborated by the morphological data set, the rbcL data set, or the combined data set, while Cyperaceae is monophyletic. Based on these results, Juncaceae s.l. can no longer be recognized without raising Prionium to family level. Juncales may consist of four families, the "Prioniaceae," Thurniaceae, Juncaceae (excluding Prionium), and Cyperaceae. The basal position of Prionium within juncales is supported by several unique features. Therefore, it is suggested that a new family should he erected for Prionium and be given the name Prioniaceae