Pollen morphology of 20 species of Euphorbioideae and one from Crotonoideae was examined with light, scanning and transmission electron microscopy. The pollen morphology presented here did not support the monophyly of Euphorbioideae, and the unique characters of tribe Stomatocalyceae such as absence of aperture margins, and thick and continuous endexine suggest the exclusion of Stomatocalyceae from Euphorbioideae which is in accordance with previous phylogenetic studies and wood anatomical data. Aforementioned pollen features in this tribe support that it is closely related to Acalyphoideae. Two subtribes of Stomatocalyceae were well recognized in terms of pollen morphology: Hamilcoinae includes species with reticulate or microreticulate exine patterns, and Stomatocalycinae includes those with perforate patterns with small supratectal elements. Three subtribes of Euphorbieae, classified in terms of pollen morphology, were further divided into three different types including perforate in Euphorbiinae, microreticulate in Neoguillauminiinae and reticulate in Anthosteminae, strongly supporting the Webster`s subtribal system. Hureae and Hippomaneae, having perforate sculpturing pattern with smooth margo, were similar in pollen morphology. Especially, the presence of small supratectal elements in Hura crepitans pollen suggests the close relationships with Excoecaria species of tribe Hippomaneae. According to the previous studies, unique intine thickness along the aperture margin in Euphorbieae was not reported elsewhere in Euphorbiaceae. However, in this study we found the same intine thickness along the aperture margin in Maprounea brasiliensis and Hura crepitans. We hypothesize that the similar intine thicknesses found in Euphorbieae and above two species are the evidence of close relationships among them.
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