Alien herbivores can have various deleterious impacts on plant communities, especially on oceanic islands where the flora tends to be dominated by endemic species. The European rabbit (Oryctolagus cuniculus L.), a polyphagous herbivore, alters plant communities through overgrazing in the areas it has invaded. In Teide National Park, a protected natural area on Tenerife (Canary Islands), rabbit herbivory is one of the main threats to the conservation of its wild flora. A microhistological study of rabbit pellets was carried out, identifying plant tissues based on cellular parameters to characterize its diet for a year in the National Park. A total of 12 plant species, mostly Canary endemics, were detected in the rabbit pellets. Despite this diversity, the diet mainly consists of three plant species: Spartocytisus supranubius, Pterocephalus lasiospermus and Descurainia bourgeauana, respectively. The latter two plant species represent a larger proportion of the diet than their coverage would suggest, potentially indicating selective foraging. This study clarifies the diet and food preferences in Teide National Park. It reveals that these rabbits consume plants previously thought to be too unpalatable, like P. lasiospermus or Adenocarpus viscosus. The data confirm the detrimental impact of rabbits on the flora of the Park and support the need to reduce the populations of this invasive herbivore, to mitigate the damage it causes. Furthermore, these results will surely contribute to designing management plans as precisely as possible, to re-establish potential plant communities and conserve existing diversity.