Leaf polymorphism of Platanus neptuni mf. fraxinifolia (Johnson et Gilmore) Kvaček et Manchester from oligocene deposits at Janda (Mt. Fruška Gora, Serbia)
2009
Djordjević-Milutinović, D., Natural History Museum, Belgrade (Serbia) | Dulić, I., NIS-Naftagas, Novi Sad (Serbia)
The rich Oligocene flora collected at Janda (Mt. Fruška Gora, Serbia) included Lauraceae, Cupressaceae and Arecaceae, a large number of trifoliolate leaves of Platanus neptuni mf. fraxinifolia. In spite of similar dimensions (3-5 cm in length and 3-4 cm in width), these leaves are very variable in structure and the shape of leaflets and may be mesomorphic or xeromorphic, lanceolate, elliptic or obovate, with distinctly or partly irregularly serrate to sub-entire margins. These differences in leaflets were used to divide these compound leaves into three groups, which show a number of transitional forms. The structure of the association of Janda makes it particularly suitable for our study, as it is simple and well-defined. There are only four types of leaves that appear in large numbers: trifoliolate compound leaves (Platanus neptuni mf. fraxinifolia); palm leaves (Sabalites and Phoenicites); laurel-like leaves (mostly Daphnogene); and conifers (Cupressaceae). From the perspective of fossilization, the presence of compound leaves of Platanus and Arecaceae is particularly interesting, as both types of leaves have a smaller probability of fossilization in normal conditions than, for example, the simple leaves of Daphnogene or a twig of Cupressaceae. The large number of tree trunks, the heavy leaves of the Arecaceae and the compound leaves of the Platanaceae indicate the possibility that this association did not fossilize during the usual seasonal deciduous season, but is due instead to immense weather-related disasters such as strong winds or floods, which tore off large masses of Platanus and palm leaves in the middle of the vegetative season and transported them to the deposition environment by great force.
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