Female reproductive system (side view)​

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I believe this adaptation of the blue poppies to their environment is due to directional selection.  Directional selection refers to the mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of the favored phenotype. In our case the plants with the thickest leaves were favored as they were more adaptable and in the end there was a shift to this characteristic by other plants.