Variation in Carpinus Betulus ( Corylaceae ) in Poland

The European hornbeam (Carpinus betulus L.) is a transitional species in the Polish flora, reaching its northeastern range limit just beyond the Polish border (Jalas and Suominen, 1976; Boratyńska, 1993). The species is a telocratic taxon which appeared in Central Europe ~5000 years ago and spread throughout Poland ~4000 years ago (Huntley and Birks, 1983; Środoń, 1993; Ralska-Jasiewiczowa et al., 2004). Isopollen maps suggest that the species migrated into Poland from at least two different directions, the southeast and west (RalskaJasiewiczowa et al., 2004). Such a migration pattern suggests that C. betulus in Poland originated from different Pleistocene refugia, and that this should be reflected in its present-day geographic variation. The variation of C. betulus nuts suggests at least the mid-Tertiary evolution of the species, and morphological differentiation much earlier than Pleistocene (Grossheim, 1940; Jentys-Szaferowa and Bialobrzeska, 1953; Jentys-Szaferowa, 1958, 1960, 1961, 1964). The two different types of nuts visible in its present-day populations have also been found in Pliocene and interglacial deposits (Jentys-Szaferowa, 1958, 1060, 1961, 1964). Isolation of western from southeastern Europe and southwestern Asia by the Paratethis Sea during the Miocene is one hypothetical reason given for the differentiation of nuts (JentysSzaferowa, 1964). The shape and dimensions of the nuts, however, are connected with characteristics of the involucres (Białobrzeska, 1966b, 1970). The present study was intended to verify the hypothesis that populations of C. betulus in southeast and central Poland came from different Pleistocene refugia. In that case, the southeastern populations of C. betulus in Poland should differ in seed scale morphology from the other populations.