Morphological characterization of sympatric and allopatric populations of Petunia axillaris and P. exserta (Solanaceae)

Floral morphological traits are frequently used to identify species, including those that are closely related and show low genetic diversity, and floral shape and colour are known to play an important role in diversification and species isolation. Floral morphology in Petunia (Solanaceae) is considered a driver of diversification because of its association with pollinators. Here, flower morphology was characterized through morphometric analyses and floral pigments. Our main aim was to determine corolla shape in populations of Petunia axillaris and P. exserta and their natural hybrids and how floral display, size and colour are involved in pollinator attraction. In addition, we investigated floral pigments in P. exserta and different hybrid classes. The results from morphometric analyses revealed that each species has a specific floral shape, independent of the collection site. By contrast, in two contact zones, a mosaic of floral phenotypes was observed with some hybrid classes based on corolla colour being placed close to P. exserta. The results suggest that several generations of hybrids or backcrossing could have given rise to this floral diversity in contact zones.