Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 90. (Budapest 1998)

Medzihradszky, Zs. ; Bajzáth, J.: The occurrence of arctic-alpine Betula species in the Hungarian Pleistocene

Nutlets (Figs 5-6). The roundish small nutlets are 1.6-1.7 mm 1.1-1.3 mm in size. The broadest part of the nutlets is above of the middle section. The wing around the body of nutlets is 0.4-0.6 mm in size. Discussion. Two fruit scales and four pieces of whole nutlets were found in the fossilassemblage. Some budscales were also recovered. These scales are more rounded than the scales of Betula nana. The top of the buds is also rounded. They are 1 x 0.75 mm in size. They are similar to Betula humilis. The distinction of nutlets of Betula nana and Betula humilis is based on the outline, the size, the ratio of the length and width of nutlets and the wing size. The two dwarf birches can be readily distinguished by the width of their wings. The wings of Betula humilis are significantly broader than those of Betula nana. If the characteristic wings are lacking, the determination of the two species is possible using numerical methods (BIALOBRZESKA & TRUCHANOWICZÓWNA 1960). Nowadays Betula humilis, similarly to Betula nana, is also a glacial relic species in the alpine-subalpine regions of Europe. Betula humilis lives in the same habitats as the other dwarf birch, mainly in bogs and moors. In addition, it also occurs in birch and alder fen carr. The occurrence of Betula humilis in the Pleistocene deposits is scarcer than that of Betula nana (RALSKA-JASIEWICZOWA 1966). It was more frequent in the territory of Russia and Belorussia in the glacials (LITVINJUK 1979). Betula pubescens ssp. tortuosa (LEBEDEV) NYMAN, 1881 (Figs 8-9) Description. Fruit scales. The fruit scales are deeply lobed and strikingly large 6x5 mm in size. The lobes are long. The space between the three lobes is narrow U-shape. Nutlets (Figs 8-9). The oboval very large nutlets are 2.5-3 mm 1.2-1.8 mm in size. The broadest part of the nutlets is in the middle section or above it. The wing around the body of nutlets is moderately broad, 0.55-0.25 mm in size. The beaks of the nutlets are long. Discussion. Two fruit scales and 12 whole nutlets and several fragments of birch tree leaves were found in the fossil assemblage. The leaf remains could not be determined at he species level. These leaves resemble Betula pubescens in the structure of the leaf margin. The morphology and the size of the nutlets and the fruit scales of Betula tortuosa differ significantly from the other birch tree, i.e. Betula pubescens. Both the fruit scales and the nutlets of Betula tortuosa are much larger than those of Betula pubescens. The occurrence of Betula tortuosa is almost as frequent in the Late glacial and early Postglacial periods as Betula nana and it also has a widespread distribution (GODWIN 1956, RALSKA-JASIEWICZOWA 1966). Most modern taxonomists regard Betula tortuosa as a subspecies of Betula pubescens, referring to the hybrid origin of this plant. In northernmost Fennoscandia (i.e. in Lapland) the mountain birch woods occupy the habitats at the forest-tundra transition. Here Betula pubescens ssp. tortuosa is the only climax tree species. Hybridization in this area is frequent and it is an important factor in the adaptation to the specific environment.