Phylogeny and Origins of Holoparasitism in Orobanchaceae
Ecology, Evolution, and Organismal Biology
• Premise: Orobanchaceae are a family of angiosperms that range from fully autotrophic and free-living to completely heterotrophic and dependent on their hosts (holoparasites). Most of the ca. 2060 species are hemiparasites that photosynthesize throughout all or part of their life cycles. Certain family members are ecologically important due to direct impacts on community biomass and diversity, plant–herbivore interactions, and nutrient cycling. Other members are among the most economically damaging weeds in the world. Multiple trophic transitions within this family make it ideal for studying molecular evolutionary and physiological changes that accompany the evolution of parasitism.
• Methods: To establish a phylogenetic framework for such work, we substantially increased taxonomic sampling at loci for which a significant amount of data already existed (nuclear ITS and PHYA, plastid matK and rps2) and added data from the low-copy nuclear locus, PHYB.
• Key results: The data provide strong support for relationships among six major clades and for the position of Brandisia hancei Hook. f. The positions ofBoschniakia himalaica Hook. f. & Thomson, Centranthera cochinchinensis(Lour.) Merr., Mannagettaea hummelii Harry Sm., and Pterygiella nigrescensOliv. are confirmed or suggested for the first time.
• Conclusions: There is a single origin of parasitism, and from within the hemiparasites, holoparasitism has originated three times. Moving from the base to the tips of the Orobanchaceae tree, the successive major splits within the parasitic clade are: Cymbarieae + the rest; Orobancheae + the rest;Brandisia + the rest; Rhinantheae + the rest; and Pedicularideae + Buchnereae.