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Aim Even though all species of Arachis (wild peanuts) develop pods underground (geocarpy), strongly limiting their dispersal ability, this genus is quite widespread in South America. Thus, our goal was to test potential explanations for how Arachis species may have achieved their current distribution. Location South America. Methods We used a dated phylogeny and 1,052 georeferenced records to run several analyses to select the variables that best explain the variation in range size in Arachis species. We tested a set of models incorporating both abiotic (age, association with rivers, niche parameters) and biotic (life span, vegetative growth, dispersal ability) factors thought to influence geographical distribution in order to select those variables that may best explain the range size of Arachis species. Results We found that no single factor was able to satisfactorily explain the geographical distribution of wild peanuts. Our results showed that Arachis range sizes are influenced by a combination of differential dispersal ability and age, although the effect of time alone was small. We also found that as Arachis species are geocarpic, their dispersal ability is positively influenced by presence of rhizomes, which improves the distances reached by individuals. Main conclusions Our research shows that the range sizes of wild peanuts are mainly constrained by differential dispersal ability and time, and they are improved by the presence of rhizomatous growth. We also advocate that applying a set of candidate hypotheses to explain species range sizes is a much better alternative than previous attempts, in which single or few hypotheses have been tested at a time.