Single phylogenetic origin of ericoid mycorrhizae within the Ericaceae

Ericoid mycorrhizae are complex organisms consisting of fungal and plant components, and their formation requires enzymatic synergisms and mutualist compatibilities resulting from cooperation of recognition and defense systems of both plant and fungus. Despite this, the plants that form this symbiosis are treated as three separate families in the Ericales: the Ericaceae, the Epacridaceae, and the Empetraceae. In this study, I used the anatomy, physiology, and symbiont compatibility of mycorrhizae (mutualistic interactions between plant roots and fungi) to formulate the hypothesis that the ericoid mycorrhiza-forming plants in the Ericaceae, Epacridaceae, and Empetraceae have a single phylogenetic origin within the Ericaceae coincident with the advent of ericoid mycorrhizae. I tested this hypothesis by parsimony analysis of newly generated and previously published partial 28S ribosomal RNA gene sequences (nuclear) and rbc-L (chloroplast) sequences obtained from GenBank. All results supported the hypothesis that ericoid mycorrhiza-forming plants have a single phylogenetic origin and indicated that the Epacridaceae and Empetraceae should be included within a broadly defined Ericaceae.