Abstract The impact of introduced ship rats (Rattus rattus) on recruitment of the megaherbPleurophyllum hookeriBuchan. (Asteraceae) was examined on subantarctic Macquarie Island, an island with no extant native terrestrial vertebrates.Pleurophyllum hookeri(Asteraceae) forms a dominant component of the Macquarie Island vegetation and is restricted to the subantarctic. The Macquarie Island population ofP. hookeriis the most extensive and intact. Introduced ship rats (Rattus rattus) are well established in tall tussock grassland of Macquarie Island. We detected rat activity for the first time withinP. hookeriherbfields, in autumn 2000. We found rats were destroying up to 90% of racemes. By excluding rats from caches of inflorescences that they had formed, we found they were having a significant negative effect on initial recruitment and seedling survival within the caches. However, because of high seedling mortality after 1 year, there was no sustained impact of the exclosures onP. hookeriseedling density.