Perspectives on the reclassification of taxa in the Arceuthobium campylopodum complex (Viscaceae)

Botany, Ahead of Print.
The taxonomic classification of dwarf mistletoes (Arceuthobium spp., Viscaceae) in series Campylopoda requires a multi-trait approach, integrating plant genetics, morphologies, and phenologies as well as their host and geographic distributions. Thus, competing interpretations on the contribution of these traits to defining species and subspecies boundaries has spurred considerable debate. Accordingly, the recent reclassification of 12 previously recognized species in ser. Campylopoda to separate subspecies of Arceuthobium campylopodum in the Flora of North America (FNA) has furthered this debate. We contend that these taxa deserve separate species recognition, while subspecies described prior to and after the recombination of ser. Campylopoda taxa in the FNA also deserve recognition. Herein, we provide evidence that the treatment in the FNA does not adequately reflect the diverse morphological, geographic, host, and phenological differences across the series, and hence, we maintain that the reclassification of ser. Campylopoda taxa was not justified according to empirical evidence published prior to and following the FNA treatment. We conclude our critique of the FNA treatment of ser. Campylopoda by advocating for the continued application of the Hawksworth and Wiens’ classification system, with minor modifications to the constitution of the series.