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

P. G. Ladd; M. E. Andrew

doi:10.1071/BT24087

RESEARCH ARTICLE (Open Access)

Previous Contents Vol 73(5)

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

P. G. Ladd

^A ^* and M. E. Andrew ^A

+ Author Affiliations

- Author Affiliations

^A School of Environmental and Conservation Sciences, Murdoch University, Murdoch, WA 6150, Australia.

^* Correspondence to: P.Ladd@murdoch.edu.au

Handling Editor: Andrew Denham

Australian Journal of Botany 73, BT24087 https://doi.org/10.1071/BT24087

Submitted: 16 December 2024 Accepted: 3 June 2025 Published: 20 June 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Parasitic plants are widespread throughout the global flora and have diverse lifestyle strategies. In most cases these plants are detrimental to the host but may have some beneficial effects on the co-occurring plants in the sourrounding communities. Some have large macroscopic plant bodies and can photosynthesise, and are therefore able to produce some fixed carbon but do take water and nutrients from the host, especially if aerially attached. Very few species have vegetative parts completely enclosed in the host, having only reproductive structures externally displayed. Whether such internal parasites have as severe effects on the host as parasites with macroscopic plant bodies is unclear.

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 6 × 30 m plots in a revegetated gravel pit in the Jurien Bay area of Western Australia.

Key results

A proportion of 21% of host plants was parasitised and these were significantly taller than unparasitised plants. These plants had 52% fewer flowers on average than unparasitised plants and subsequently far 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.

Keywords: Apodanthaceae, Daviesia, endoparasite, Fabaceae, holoparasite, Pilostyles, reduced flowering, reduced fruits.

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