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Reductions in fitness due to an endoparasitic plant are comparable to the impacts of hemiparasites

Philip Ladd , Margaret Andrew

Abstract

Context. Parasitic plants are widespread throughout the world flora and have a diversity of life style strategies. In most cases they are detrimental to their host but may have some beneficial effects on the co-occurring plants in the communities in which they grow. Some have large macroscopic plant bodies and can photosynthesise, so are able to produce some of their own fixed carbon, but do take water and nutrients from the host, especially if they are aerially attached. A very few species have vegetative parts completely enclosed in the host, having only reproductive structures externally displayed. It is unclear if such internal parasites have as severe effects on their host as parasites with macroscopic plant bodies. Aims. The endoparasite Pilostyles hamiltoniorum infests pea species (predominantly Daviesia species) in the south west of Western Australia. We investigated the effect of this parasite on the vegetative growth and reproduction of Daviesia angulata in heathland vegetation. Methods. Size, flowering and fruiting of parasitised and unparasitised host plants were recorded in three 6x30m plots in a revegetated gravel pit in the Jurien area of Western Australia. Key results. 21% of host plants were parasitised and were significantly taller than unparasitised plants. They had 52% fewer flowers on average than unparasitised plants and subsequently many fewer fruits. Conclusions. The reduction in reproductive output by this internal parasite was at least equal to or more severe than occurs in published examples of decreased productivity of other species parasitised by species with macroscopic plant morphology. Implications. The reduced reproductive output of the host plants would be inimical to seed stores in the soil that this species relies on for regeneration after fires that commonly affect the vegetation in this region.

BT24087  Accepted 03 June 2025

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