The evolution of parasitism in scrophulariaceae/orobanchaceae: Plastid gene sequences refute an evolutionary transition series

Parasitic plants in Scrophulariaceae and Orobanchaceae have been traditionally depicted as forming a linear evolutionary series beginning with hemiparasitism and ending with holoparasitism. The genera Lathraea, Harveya, and Hyobanche have been viewed as transitional links between the parasitic members of Scrophulariaceae and the strictly holoparasitic habit of the traditional Orobanchaceae. Phylogenetic analyses of plastid rps2 and mark sequences were performed. The transitional genera are not transitional to the traditional Orobanchaceae, but represent multiple independent origins of holoparasitism. Within Scrophulariaceae, the two traditional subfamilies Rhinanthoideae and Antirrhinoideae are defined by the arrangement of the corolla lobes during aestivation. However, neither of the two subfamilies is monophyletic in our analyses, suggesting that corolla lobe position is a homoplastic character. While the traditional Orobanchaceae are monophyletic, tribes Buchnereae and Rhinantheae are clearly not, and genus Orobanche probably is not. Clades of parasitic genera correspond well with biogeographic provinces. One strongly supported clade contains the parasitic Scrophulariaceae, the traditional Orobanchaceae, and Lindenbergia. It is proposed that this clade be defined as the Orobanchaceae.