Systematic relevance of the pollen morphology for the Rondeletia complex (Cinchonoideae, Rubiaceae)

Seventeen morphologically related genera have been considered as the Rondeletia complex, traditionally in Rondeletieae. Molecular studies agree that this is a polyphyletic group and some genera have been transferred to Guettardeae. Nevertheless, no solid morphological characters support this hypothesis. Our aim is to explore pollen morphology to see if this source of characters has systematic value. Our study uses light and scanning electron microscopy for 30 species of both tribes representing 14 genera. The most important characters are polar outline, endoaperture type and nexine discontinuities. Our results do not permit diagnosis of tribes, but they show that the genera formerly included in the Rondeletia complex, but now placed in Guettardeae, have nexine discontinuities in polar areas: endofissures (Rogiera) or endocracks (Arachnothryx complex: Arachnothryx-Gonzalagunia-Javorkaea-Renistipula). Palynological data also confirm a close relationship of Rondeletia with Stevensia, corroborating their synonymy, and of Arachnothryx with Gonzalagunia-Javorkaea-Renistipula, providing evidence of their close relationship. We conclude that pollen is a useful source of characters for supporting main lineages, but further research is still necessary for other genera, including Blepharidium, Machaonia, Mazaea and additional Rondeletia spp.