Phylogeny and patterns of species diversification in Rafflesia

Rafflesia is a genus of flowering plants of the tropical rain forests that includes the largest flowers in the world ranging from 10 up to 100 cm in diameter-sizes unlike any other flower. The Rafflesia flower has been symbolic of plant conservation in the tropics. Members of Rafflesia are haustorial holoparasites; they lack leaves, stem, or roots, and without chlorophyll. They have very specific host plants, preferring only species of the vine genus Tetrastigma (wild grape family). Rafflesia is restricted to South East Asia where at least 23 species have so far been described and recognized (including nine species from the Philippines) whose relationships remain poorly understood. There have been significantly changes in our understanding of the phylogeny of flowering plants with increased use of molecular data, especially DNA sequence data. However, phylogenetic relationships of parasitic plants, including Rafflesia, has long been problematic because of the loss of diverse organs such as leaves, perianth parts, and integuments, as well as, the loss of chlorophyll, and highly modified plastids genomes that lack many genes or have accelerated rates of molecular evolution and deletions not in triplets - characters that are associated with the parasitic habit. Research using sequences of the mitochondrial gene matR and nuclear SSU rDNA, as well as, nuclear 18S and phyC, found evidence for placing Rafflesia in the order Malpighiales. But this position within the order was nuclear due to either insufficient taxon sampling or a lack of phylogenetic signal. Further molecular analyses using five mitochondrial genes (ccmC, ccmB, cob, nad6, matR), and one chloroplast gene (matK), and nuclear (nr) small-and large-subunit ribosomal DNA, clearly and robustly showed that Rafflesia (and Rhizanthes, and Sapria) are nested with the family Euphorbiaceae in Malpighiales. If this hypothesis is confirmed, in order to maintain the monopoly of Euphotbiaceae, either the basal clade represented by Pogonophora, Pera, and Clutia in the dendrogram will have to be split off as a separate family (Pera is recognized in the separate family Peraceae in some classifications), or Rafflesiaceae will have to be included as a subfamily in the Euphorbiaceae.