Comparison of morphological characters and molecular markers for the analysis of hybridization in sessile and pedunculate oak

Interspecific hybridization is common in many plant groups, but the morphology of hybrids has rarely been studied on an experimental basis. The sessile and the pedunculate oak are closely related species which can hybridize in nature. Yet, the morphology of their hybrids is still a matter of conjecture. Here we studied the morphology and the hybridization rate in several open-pollinated progenies collected in a mixed stand of sessile and pedunculate oak. For both species, two types of pollinating environments (intraspecific and interspecific) were compared for their morphological and genetic effects in progenies. The analysis of the molecular markers showed that the contribution of sessile oak to the progenies of pedunculate oak was positive. The genetic effect of the pollinating environment was significant. The morphological characters gave a better image of interspecific gene flow when considered together in multivariate analyses rather than in univariate analyses. This probably occurred because the hybrids were a mosaic of parental and intermediate characters, rather than exactly intermediate forms.