A greenhouse bioassay was carried out to determine the mycorrhizal dependency of alcaparro (Senna pistaciifolia Kunth). A randomized complete experimental design was employed, with six treatments in a factorial arrangement 3x2; the treatments consisted of three levels in soil solution phosphorus (P) (0.002, 0.02, and 0.2 mg L-1) combined with two levels of mycorrhizal inoculation either uninoculated or inoculated with Glomus agreggatum. The variables studied were leaf P content as a function of time, shoot dry matter, shoot P content, mycorrhizal colonization of roots, and the mycorrhizal dependency (MD). The results indicate that the leaf P content increased significantly with the mycorrhizal inoculation in alcaparro to 0.02 mg L-1 after the second sampling days, but not in the other soil P levels. Likewise, shoot dry weight increased significantly at 0.02 mg L-1. On the other hand, the total plant P content increase at all levels of soil available P. The mycorrhizal colonization in alcaparro roots was 11, 23, and 0% at 0.02, 0.002 and 0.2 mg of P L-1, respectively. The MD for alcaparro was 32%, which allow classify this specie as moderately dependent on the mycorrhizal association.