GENETIC, MORPHOLOGICAL, ECOLOGICAL AND PHENOLOGICAL DIFFERENTIATION BETWEEN QUERCUS-PETRAEA (MATT) LIEBL AND QUERCUS-ROBUR L IN A MIXED STAND OF NORTHWEST OF FRANCE

The sessile and pedunculate oaks are the most common tree species in E urope. The 2 taxons are closely related, and, in spite of their ecolog ical differences, they form frequently mixed forests, where hybridisat ion is suspected to occur. In this paper, we describe a mixed forest s tand of sessile and pedunculate oaks, in which a regular slope establi shes an ecological gradient. Genetic, morphological, phenological and ecological differentiation between the 2 species and the existence of parallel variations among these different types of characters are anal ysed. The sessile and the pedunculate oaks studied here showed a weak differentiation for the genetic, morphological and ecological characte rs. The flowering of the 2 species was synchronous over 3 years. Morph ological and ecological traits showed an overlapping distribution; wit h allozymes any specific marker was not identified. Within each specie s the diversity is not structured along the ecological gradient, we do not find associations among ecological, morphological, phenological t raits and allozyme markers. Inferences about the taxonomic relationshi ps of these species are discussed.