Parasitic plants show striking convergence in host preference across angiosperm lineages.

Background And Aims: The host specificity of a parasite underpins its ecology, distribution, invasive potential and adaptability, yet for most parasitic plants the host ranges are poorly understood. We examine host-parasite relationships across lineages to infer how host specificity might have influenced the evolution of parasitism in plants.

Methods: Host preference data for all plant holoparasite species were collected manually from literature and herbarium specimens, then analysed to investigate and visualize host diversity and specificity.

Key Results: We reveal a disproportionality in host preference across host lineages: the Asteraceae contain 10 % of angiosperm diversity but are infected by 31 % of parasite species; meanwhile, monocots comprise 23 % of angiosperm diversity but are infected by only 3.2 % of parasite species of parasite species. Furthermore, we observe striking convergence in host preference: Asteraceae, Euphorbiaceae and Fabaceae are infected by six, five and four independent parasite lineages, respectively. We also demonstrate considerable variation in the degree of host specificity among closely related parasite species; a result that does not reflect the expectation of holoparasites (especially endoparasites) as host specialists.

Conclusions: The marked pattern of convergence in preference across disparate lineages points to a common pathway in the evolution of parasitism of eudicots in preference to monocots, which might, in turn, have been driven by a divergence in host root and vascular architecture. The unexpected variation in host specificity among closely related species suggests that even apparent generalists might contain cryptic host-specific taxa. This highlights the value of host preference as an additional consideration in parasitic plant taxonomy. Together, our data point to a complex interplay between ecological and physiological factors driving the evolution of host-parasite interactions. Moreover, they emphasize how little is known about the ecology of most holoparasitic plants, a group of organisms that are especially vulnerable at a time of unprecedented biodiversity loss and extinction.