Plastome and nuclear phylogenies of dwarf mistletoes (Arceuthobium: Viscaceae)

Dwarf mistletoes are a group of morphologically-reduced aerial shoot parasites of Pinaceae and Cupressaceae found in the northern hemisphere and equatorial east Africa. Though diagnosable by a suite of morphological traits, phylogenetic knowledge of species relationships has been limited to studies employing either comprehensive sampling of one or two genes, or more sequence data but limited taxonomic sampling. We used genome skimming data to assemble 3kb of the nuclear ribosomal cistron and up to 45kb of the plastome to clarify the phylogenetic root of the genus, species monophyly, and relationships among infraspecific taxa. Genomic differentiation among taxa was variable; however, we found strong support for reciprocally monophyletic New World and Old World lineages and congruent nrDNA and plastome topologies at the species level and below, and most taxonomic sections and at the species level and below. Plastome gene content was stable across the genus with minimal pseudogenization or loss, with the notable exception of cemA. These findings form the basis of our re-evaluation of historical biogeographical hypotheses, species and subspecies-level taxonomy, and plastome evolution in Arceuthobium. More broadly, this work provides a foundation for future clade-focused comparative and biosystematics studies of Arceuthobium.