(1) A field study was conducted in the Mojave Desert to determine the horizontal distribution of two co-dominating species and the degree of interference between individuals of the same species and of different species. (2) Variance/mean analyses indicated that one of the co-dominating species (Larrea tridentata) is regularly distributed and the other (Ambrosia dumosa) is contagiously distributed. (3) The results of a controlled removal experiment showed that water-related interference does occur at this site when water availability is low, and that at present, interference between species is usually more intense than that within a species. These results, together with nearest-neighbour analyses, revealed that regular distributions [...]