The distribution and micromorphology of vestured pits in secondary xylem of eleven species representing genus Fraxinus were investigated in details by means of SEM.Richness indexes of intervascular vestured pits and quantitative features of the bordered pits were measured on SEM images using software Carnoy 2.0.Scanning electron microscopy illustrates that vestured pits in the vessel elements of secondary xylem of studied species varied considerably in distribution and micromorphology,and the statistic description of richness indexes further confirmed the great variable distribution of vestured pits.Stepwise regression analysis between respective richness indexes and quantitative features of the bordered pits indicated that 2 out of 3 richness indexes including frequency of vestured vessel outer aperature and frequency of vestured vessel pit chamber increased significantly with increasing Fap (aperture fraction),suggesting that richness of vestured pits was correlated with geometric structure of the bordered pits.It can be inferred that consistent occurrence of vestured pits in genus Fraxinus from the common presence of the vestured pits in studied species.Therefore,the occurrence of vestured pits can delimit the genus Fraxinus.