Cannibal plants: intraspecific autoparasitism among host-specific holoparasites

Intraspecific autoparasitism, the phenomenon in which a parasite serves as the host for another individual of the same species, is a well-described interaction among hemiparasitic flowering plants. Here, I describe a rare case of autoparasitism in Epifagus virginiana (L.) W.P.C. Barton (Orobanchaceae), a holoparasitic plant normally found exclusively on the roots of Fagus grandifolia Ehrh. (Fagaceae). Confirmation of the autoparasitic relationship was obtained through microtomography and anatomical analyses. Results show the presence of vessel connections between the two E. virginiana plants and the unobstructed passage of solutes from one plant to another, thus suggesting the autoparasitic connection to be fully functional. While several segments of nearby host roots were entangled with the adventitious roots of the parasite, no parasite–host vascular connection was detected. Additionally, an analysis of digitized herbarium specimens showed that albeit rare, the observed autoparasitic relationship in E. virginiana is not a one-of case. A total of 3097 digitized herbarium specimens were also analyzed, among which 1.69% were observed to potentially include an autoparasitic connection. Altogether, these results provide new clues for the investigation of host-specificity and haustorium development processes in parasitic flowering plants.