Pollen morphology of Miliusa and relatives (Annonaceae)

In order to provide additional data for the subdivision of the palaeotropical genus Miliusa (Annonaceae), its pollen was examined using light, scanning and transmission electron microscopy, including 20 of the 30 - 40 species. Further, species of the other genera in the former tribe Miliuseae (Alphonsea, Mezzettia, Orophea, Platymitra; Phoenicanthus not available) and of the Polyalthia cerasoides group, the sister group to Miliusa in a recent molecular analysis, were included. The pollen of Mezzettia and Platymitra is described for the first time with scanning and transmission electron microscopy. The pollen of all species studied with transmission electron microscopy appeared to possess an inaperturate exine, but apertural areas ('germination zones') were observed in the intine. The pollen morphological variation within Miliusa does not correlate with the macromorphological subdivision of the genus. It appeared to be impossible to define distinct pollen types. The former tribe Miliuseae cannot be characterised or subdivided with the help of pollen characters either. All genera fit in the larger miliusoid clade (25 genera). The pollen of the Polyalthia cerasoides group deviates in its finely and densely granular infratectum.