THE POLLEN FROM THE TRIBE ACALYPHEAE (ACA LYPHOIDEAE, EUPHORBIACEAE)

The pollen of 27/30 genera and 48/1300 species of the tribe Acalypheae have been studied by means of L.M. and S.E.M. Variations in the chara cter of the apertures and in the sculpturing elements allow a characte rization into eleven subtribes. The pollen is generally colporate and mostly has small nexine thickenings around the apertures. The genera S ampantaea and Dysopsis are the only exceptions to this having pollen w ith three very narrow ectoapertural simple furrows. The tectum is perf orate and has microspines or micropapillae around the perforations, wi th the exception of some rare species in which the sculpturing is stri ate (Micrococca scariosa, Homonoia javanensis) or reticulate (Amyrea, Mareya longifolia, Seidelia). The pollen of the Acalypheae belong to t wo great types: 1 degrees the tectum is widely perforate and the grain s are generally longiaxe; 2 degrees the tectum is scarcely microperfor ate and the grains are often breviaxe. The variations in the pollen ch aracters: a decrease in the tectal perforations, and a great reduction in the ectoaperture and/or the endoaperture which can even disappear, are correlative with those of the flower and its type of pollination. The pollen of the Acalypheae clearly resembles that of the three near est tribes of the Acalyphoideae. Similarities with the Crotonoideae an d the Phyllanthoideae are evident except for the placement of the free elements on the exine.