Competitive relationships existing between two closely related species of Argemone living in the same area.

The present paper deals with the reaction of two closely related species of Argemone L., A. mexicana L. and A. ochroleuca Sweet, to its own density in pure stands and a comparison of this with its reaction to the density of the associated species. The results of the pure culture studies indicate that whilst each of the two species reacted to an increase in its own density by higher mortality and a striking reduction in vegetative and reproductive growth, A. mexicana was more susceptible to intraspecific effect than A. ochroleuca. On the other hand, mixed culture studies indicated that A. mexicana was more successful when in competition with A. ochroleuca. Further, that species which was in a majority in the mixture suffered most compared to the minority species. Such a density dependent differential behaviour in pure stands and frequency dependent differential behaviour in mixed cultures along with the reversal in superiority of the two species in pure and mixed cultures was considered to be responsible for the cohabitation of the two species and their relative population sizes in nature.