The morphometrics of autopolyploidy: insignificant differentiation among sexual–apomictic cytotypes

Polyploidization of the plant genome affects the phenotype of individuals including their morphology. In autopolyploids, we expect mainly nucleotypic effects, from a number of monoploid genomes (i.e. chromosome sets) or genome sizeNucleotypic effects on the morphology and the anatomy of plants are observed on different organizational levels. Cell size increases in tendency with ploidy level or genome size. At the tissue level, quantitative changes like the density of stomata or hairs have been reported, while at the organism level polyploidization can be associated with an increase in the organ size (like flowers or leaves) or in whole individuals. Although we have known about the phenomenon of autopolyploidy for a long time, there are astonishingly few detailed quantitative studies on associated morphological variation.

In a recent study published in AoBP, Bigl et al. morphometrically analysed five ploidy cytotypes of the rosaceous species Potentilla puberula (a member of the Potentilla verna aggregate). The authors found that these cytotypes did not significantly differ from each other morphologically, supporting the notion that autopolyploids usually resample the morphospace of their ancestors. However, nucleotypic effects were observed that conferred to an increase of the overall size of individuals with ploidy. The authors finish by critically discussing these results in the context of postpolyploidization effects and the modificatory influence of the environment, factors known to modify the morphology of cytotypes, and conclude that cytotypes are best treated as intraspecific variants within a single species.