Parasitic plants show striking convergence in host preference across angiosperm lineages

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.

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.

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.

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.