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-Leaf morphology was assessed in nine mixed oak stands (Quercus petraea and Q. robur) located in eight European countries. Exhaustive sampling was used in an area of each stand where the two species coexisted in approximately equal proportions (about 170 trees/species/stand). Fourteen leaf characters were assessed on each of 5 to10 leaves collected from the upper part of each tree. Three multivariate statistical techniques (CDA, canonical discriminant analysis; PCA, principal component analysis; MCA, multiple correspondence analysis) were used in two different ways: first on the total set of leaves over all stands (global analysis) and second, separately within each stand (local analysis). There was a general agreement of the results among the statistical methods used and between the analyses conducted (global and local). The first synthetic variable derived by each multivariate analysis exhibited a clear and sharp bimodal distribution, with overlapping in the central part. The two modes were interpreted as the two species, and the overlapping region was interpreted as an area where the within-species variations were superimposed. There was no discontinuity in the distribution or no visible evidence of a third mode which would have indicated the existence of a third population composed of trees with intermediate morphologies. Based on petiole length and number of intercalary veins, an "easy to use" discriminant function applicable to a major part of the natural distribution of the species was constructed. Validation on an independent set of trees provided a 98% rate of correct identification. The results were interpreted in the light of earlier reports about extensive hybridization occurring in mixed oak stands. Maternal effects on morphological characters, as well as a lower frequency or fitness of hybrids in comparison with parent species could explain the maintenance of two modes, which might be composed of either pure species or pure species and introgressed forms. morphology / leaf / Quercus robur / Quercus petraea / taxonomyRésumé -La différenciation morphologique des feuilles entre Quercus robur et Quercus petraea est stable à travers les peuplements mé-langés de chênes de l'ouest européen. La variabilité de la morphologie foliaire a été etudiée dans neuf peuplements mélangés de chênes (Quercus petraea et Q. robur) en Europe sur la base d'un échantillon exhaustif moyen de 170 arbres/espèce/peuplement. Trois méthodes d'analyses multivariables ont été utilisées (ACD : analyse canonique discriminante ; ACP : analyse en composantes principales ; AFC : analyse factorielle des correspondances). Les trois méthodes aboutissent à des résultats congruents. La première variable synthétique de chaque méthode se Ann. For. Sci. 59 (2002)

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Variation in the non-coding region of chloroplast DNA (cpDNA) was studied to determine the route and pattern of postglacial recolonisation of native oak throughout mainland Britain. In total, 1076 mature oak trees of either Quercus petraea (Matt.) Liebl. or Quercus robur L. from 224 British ancient woodland sites were analysed, and represent the largest and most saturating molecular analysis of British oak undertaken to date. The majority of oaks (98%) possessed one of the three cpDNA haplotypes from lineage B that are commonly found in Spain and western regions of France. Thus, our findings strongly support the hypothesis that most native British Q. robur and Q. petraea originate from a Pleistocene refugium in the Iberian Peninsula. A haplotype previously thought to be the result of a de novo postglacial mutation in East Anglia, Native and Nonnative in British Forestry. Proceedings of a Discussion Meeting, March 31-April 2, 1995. University of Warwick, pp. 38-55] was found at several sites in eastern Britain, including major population clusters in East Anglia, Tyneside and northeast Scotland. We propose that this haplotype was introduced to Britain via normal postglacial colonisation processes. Less than 2% of oak trees sampled possessed haplotypes from lineages which originate from more eastern refugia (Italy and Balkans). Whilst human-mediated translocation may be responsible for the occurrence of these haplotypes in Britain, single long distance dispersal events (of between 300 and 500 km from France) cannot be excluded for at least one case. The majority of populations sampled (including those where both species are present) were fixed for a single haplotype (69%). However, significant areas of mixed haplotype woods occurred in the Welsh Marches and Scotland and the proportion of population fixation was lower and intra-population diversity higher for Q. robur (G ST ¼ 0:661; h S ¼ 0:224) than for Q. petraea (G ST ¼ 0:884; h S ¼ 0:089). The distribution of cpDNA variation in British oak populations is discussed and interpreted in the light of hypothesised recolonisation routes and dynamics, inter-specific hybridisation and chloroplast capture, and human impacts due to the management of ancient woodland. #