Evolution of Impatiens (Balsaminaceae) in the Albertine Rift – The endemic Impatiens purpureoviolacea complex consists of ten species

Abstract

The Albertine Rift harbours a highly diverse flora with numerous endemic species. An important component of the forestunderstorey is the herbaceous genusImpatiens. Fieldwork in Burundi, the Democratic Republic of the Congo and Rwanda as well asmorphological studies indicated that the Albertine Rift endemicImpatiens purpureoviolacearepresents a species complex. We ana-lyzed the hidden diversity of the complex using morphological and molecular data supplemented by herbarium studies. We found thattheImpatiens purpureoviolaceacomplex can be divided into morphologically and phylogenetically well characterized clades contain-ing ten species and a natural hybrid. We describe all of these species, provide a species key and analyze their evolutionary history.BesideImpatiens purpureoviolaceaandI. gesneroidea, the already describedI. urundiensisis resurrected from synonymy. Two va-rieties,Impatiens purpureoviolaceavar.longicalcarataandI. gesneroideavar.superglabraare raised to species status, and five newspecies (Impatiens elwiraurzulae,I. lotteri,I. ludewigii,I. lutzmannii,I. versicolor) and a new natural hybrid (I. ×troupinii) are de-scribed. Within the mostly insect-pollinated species of the clade, two bird-pollinated species (Impatiens gesneroidea,I. super-glabra) evolved independently. The clade split from its sister taxon in the Pliocene and started diversifying during the Pliocene/Pleistocene transition in parallel to an increased mountain uplifting and volcanic activity in the Albertine Rift. It further diversifiedduring the Pleistocene, likely due to the changes in forest cover and connectivity induced by climatic fluctuations.