New insights into the origin of two new epiphytic Impatiens species (Balsaminaceae) from West Central Africa based on molecular phylogenetic analyses

During recent fieldwork activities conducted in order to complete the publication of the Flora of Gabon, new material was collected of two previously unknown Impatiens species. Molecular phylogenetic analyses and a detailed comparative morphological study confirmed the status of the newly collected material. Impatiens wilksiana Stevart, S.B. Janssens & Eb. Fisch. is characterized by a dense racemose inflorescence, rather small flowers, yellow petals and red sepals, whereas I. issembei S.B. Janssens, Stevart & Eb. Fisch. has few-flowered racemose inflorescences and larger flowers, which are entirely vivid-red. The divergence of I. issembei and wilksiana is estimated at 0.96 Ma ago, an age that corresponds with a shift towards increasingly variable drier conditions situated between 1.2 and 0.8 Ma ago. During this period, the once continuous ancestral population of I. issembei and I. wilksiana was probably fragmented into two sister populations restricted to the forest refuges in the Massif du Chaillu and the Monts de Cristal. Allopatric speciation in association with such refuges may have played a role in the origin and diversification of the present day African Impatiens.