Question: What is the role of Stipa tenacissima as a nurse plant of the rare and threatened endemic species Haplophyllumbastetanum?

Location: Semi-arid steppe of the Guadix-Baza basin (SE Spain).

Methods: In the two H. bastetanum populations known, we (1) estimated the number of individuals and (2) analysed the influence of the factors ‘site’ (S1 = Hernán Valle, S2 = Alicún), ‘microhabitat’ (inside and below the canopy of the S. tenacissima tussocks vs. open areas), ‘life stage’ (vegetative, reproductive), ‘aspect’ (N, S, E, W, flat) and ‘damage’ (yes or no), in relation to the distribution of individuals and to the height, number of flowers, number of capsules, and edaphic variables.

Results: The total number of individuals was estimated at 3135. S. tenacissima was found to have a positive and significant effect on the distribution of H. bastetanum, more pronounced in the sample taken at S2 than S1, where 83.8% of the plants were growing in association with S. tenacissima. Similarly, there were more H. bastetanum individuals that became reproductive inside S. tenacissima tussocks than in the open areas, and H. bastetanum individuals had a greater production of flowers and fruits, especially in the sample taken at S1. Organic carbon, nitrogen, and carbon:nitrogen ratio were related to the height and number of flowers and capsules of the plants.

Conclusion: Although new patches were established, with a larger number of individuals, H. bastetanum continues to be Critically Endangered (CR). The results support the hypothesis of the facilitation effect of S. tenacissima on this rare, endemic species. Facilitation of species of interest in conservation is an aspect that has not previously been clearly reported. We propound this important process as a valuable tool for rehabilitation of populations of threatened plant species in conservation biology projects.

Nomenclature: Castroviejo (1986–2003); Valdés et al. (1987).