Impatiens smetsiana, another example of convergent evolution of flower morphology in Impatiens

Abstract

Background and aims – The genus Impatiens is known for its enormous convergent phenotypic adaptation, with similar floral traits having independently evolved in distantly related lineages. The large functional convergence of Impatiens flowers causes a high degree of homoplasy for several phenotypic characters resulting in increased difficulties to distinguish between species with a similar morphology that are only distantly related, however. As a result, some species remain under the radar, as they are confused with other well-known species. This was the case for a new Impatiens species from the Tchabal Mbabo Mountains in Cameroon – Impatiens smetsiana – that was initially mistaken for the morphologically similar species I. erecticornis, an endemic from Central East Africa. Material and methods – A combined molecular-morphological approach was applied in which phylogenetics (ITS, ImpDEF1, and ImpDEF2), biogeography, and age estimation analyses were combined with morphological data on floral and vegetative structures. Key results – In this study, we demonstrate the close affinity of the newly collected material with a group of Equatorial West African species, including I. filicornu, I. nzabiana, I. oumina, and I. kamerunensis. The present finding represents a clear case of convergent evolution in which two distantly related taxa independently converged on practically the same flower morphology. Conclusion – Within Impatiens, several examples of floral homoplasy have been observed yet not in such a clear way. The convergent evolution of the flowers of I. smetsiana and I. erecticornis is undoubtedly closely correlated with an adaptation to a similar pollination syndrome.