Morphological diversity of functionally distinctive floral organs in Iris pumila: Does the flower color matter?

Abstract

Flowers are complex phenotypic structures composed of four functionally distinct organs arranged in concentric floral whorls: sepals in the frst, petals in the second, and two inner whorls consisting of reproductive structures: stamens in the third whorl and tricarpellary gynoecium, in the centre. Color, size and shape of these floral organs are considered to be important signals that can attract the pollinators, advertising the plants’ floral reward (commonly nectar and pollen). Here we use the methods of geometric morphometrics to compare size and shape variation of three functionally different floral organs: falls, standards and style arms, among fve distinct color morphs (blue, violet, dark blue, dark violet and yellow). Pairwise comparisons of the centroid size means showed that all floral organs differed signifcantly among the analysed color phenotypes. The mean shape of falls, standards and style arms appeared to be flower color-specifc as well, but most noticeably between yellow - on one side, and blue/violet morphs - on the other. Procrustes ANOVAs revealed the signifcant presence of directional and fluctuating asymmetry for falls and standards among all fve color morphs, with the exception of style arms. The observed morphological diversifcation of floral organs among distinctive I. pumila color phenotypes could be the adaptive outcome of the interactions with their pollinators.