Abstract: The genus Trigonobalanus consists of three species which are disjunctly distributed in Asia and South America. Pollen grains of T. doichangensis (Camus) Forman, T. verticillata Forman and T. excelsa G. Lozano, J. Hdz-C. et J. He-nao were examined under light microscope (LM), scanning electron microscope (SEM), laser scanning confocal imagine system(MRC-600) and transmission electron microscope(TEM). Pollen morphology of these species of Trigonobalanus showed great variation in shape, aperture position and structure of exine. The pollen morphology of Trigonobalanus may be divided into three types: (A)Pollen grains of T. doichangensis are suboblate, with P/E=0.88～0.96, broad elliptic in equatorial view, obtusely triangular in polar view; 3-colporate, goniotreme, vestibulate and thickened on margin; the exine 2-layered, the thickest in aperture area, tectate-imperforate, verrucose-rugulose (SEM). (B) Pollen grains of T. excelsa are prolate, with P/E = 1.23 ～1.55, long-elliptic in equatorial view, trilobate or subtriangular in polar view; 3-colporoidate (3-colpate), pleurotreme (pretrime); tectate-perforate, crass-tuberculate or verrucose (SEM). (C) Pollen grains of T. verticillata are subsphaeroidal with P/E = 1.10～1.18, subcircular in equatorial view, trilobate-circular in polar view; 3-colporate, pleurotrime; tectate-perforate, fine-tuberculate or vermiculate short-striate (SEM). The pollen morphology of the three species of Trigonobalanus well supports the view-point of Nixin and Crepet to treat them as three monotypic genera, i.e. Formanodendren (F. doichangensis(Camus) Nixon et Crepet), Colombobalanus (C. excelsa (G. Lozano, J. Hdz-C. et J. Henao)Nixon et Crepet) and Trigonobalanus (T. verticillata Forman). Theresults also show that the three genera are closely related to Fagus and Ouercus.

Key words: Pollen morphology, Trigonobalanus, Colombobalanus, Formanodendren,