2019 ASHS Annual Conference

Abstract: The phenotypic diversity of floral organs plays an important role in the study of plant taxonomy and genetic evolution. Previous studies had concentrated on the direction of evolution, but not the degree of evolution. Box plot and frequency distribution function method were applied and evolutionary rules of the phenotypic traits of floral organs in Malus species and cultivars were explored in three dimensions of numeric value, size, and morphology. With respect to the direction of evolution, the floral organs showed a consistent trend of quantitative petaloid conversion (pistils or stamens → petals), size miniaturization (large → small), and morphological narrowness (petal shape: circular → elliptic; sepal shape: triangular → lanceolate) by both methods. In term of the degree of evolution, frequency distribution function analysis revealed clearer evolutionary changes than the box plot method in Malus taxa, which were characterized by size traits > quantitative traits > morphological traits and by horizontal dimensions > radial dimensions. Our findings suggested that the frequency distribution function analysis should be sensitive to reveal both the direction and degree of evolutionary changes in phenotypic traits of floral organs. We can construct a putative flower types for Malus breeding and provide a quantitative method for future evaluation of evolutionary rules among different populations in the plant world.

key words: Malus spp.; floral traits; evolutionary degree; evolutionary direction; frequency distribution