A total evidence approach using palynological characters to infer the complex evolutionary history of the Asian Impatiens (Balsaminaceae)

The present study contributes to a better understanding of major palynological trends in Impatiens, one of the largest genera in angiosperms, and evaluates the phylogenetic usefulness of pollen morphological characters in the genus. The pollen morphological diversity of 115 Asian species of the genus was investigated using light microscopy and scanning electron microscopy and analyzed in a phylogenetic framework using Bayesian inference and Bayesian posterior character mapping as well as parsimony character optimization. Despite the rather young age of Impatiens and its extremely rapid radiation, a striking palynological variability could be observed. The ancestral pollen type in Impatiens is a triangular, tri-aperturate pollen grain with reticulate sexine ornamentation, which subsequently evolved into the main Impatiens pollen type: a 4-aperturate, rectangular pollen grain with a reticulate sexine ornamentation. The most recently diversified Asian clades are characterized by several reversions from 4-aperturate to 3-aperturate and changes in sexine ornamentation from reticulate to microreticulate sexine ornamentation. Also differences in pollen view can be observed amongst the most recently diversified Asian lineages ranging from circular, quadrangular, elliptic to sub-elliptic and rectangular. Although some pollen morphological characters seem to be homoplasious, others help to improve the resolution of some phylogenetically problematic lineages in the genus.