The phenomenon of morphological intermediacy often can be used to identify individuals of hybrid origin. However, morphological intermediacy is not always apparent in individual characters. Our experience is that multivariate analyses are very likely to reveal hybridity because the combinations of characters in the hybrids disrupt the patterns of covariance that allow recognition of the parental taxa. For this study, we sampled six trees (two each from three accessions) of Acer X freemanii from the Morton Arboretum, along with 40 trees from northern Indiana field identified as either A. rubrum or A. saccharinum. Leaves were pressed and dried and leaf blade outline and landmark data were captured using MorphoSys. A data set of linear and angular characters was used for input to cluster analysis and principal components analysis. The same multivariate tools were used to analyze elliptic Fourier coefficients derived from leaf outlines and thin-plate spline weights derived from landmark configurations. All three approaches provide views in which some or all of the hybrids are intermediate between the parental taxa and in which some field-collected trees also appear to be of hybrid origin. But, there are differences with respect to which trees may be of hybrid origin. These differences reflect the different aspects of leaf blade shape derived from each set of data.

Key words: Acer, hybrids, morphometrics, multivariate analyses