Evolutionary trends in the morphology and harmomegathy of the pollen of the genus Guioa (Sapindaceae-Cupanieae)

A pollen morphological survey of the genus Guioa is presented. Based on a study of the harmomegathy in relation to morphological series, evolutionary trends are postulated: 1. wide ectoapertures → narrow ectoapertures 2. grain parasyncolporate → grain colporate 3. grain parasyncolporate → grain syncolporate 4. ornamentation rugulate → ornamentation psilate-imperforate. It is suggested that the most ‘primitive’ species of Guioa occur in the southeastern part of the distribution area of the genus. Guioa can be subdivided into four poorly delimited pollen morphological groups. Its affinities to other genera in the Cupanieae are briefly discussed. Pollen of the most ‘primitive’ group is similar to that of several ‘primitive’ genera (e.g. Arytera, Matayba, Molinaea, and Tina) in the tribe.