The genus Birisia (Dicksoniaceae) in Cretaceous flora of Siberia and North-East of Russia
In the result of the re-examination of type material of the genus Birisia from the Cretaceous deposits of Siberia and North-East of Russia, we include only three species in this genus: B. alata (Prynada) Samylina (early-middle Albian - Coniacian), B. onychioides (Vassilevskaja et Kara-Mursa) Samylina (Aptian), and B. acutata Samylina (early-middle Albian). Species B. ochotica and B. alata are united under the name B. alata. Species B. jelisejevii, B. samylinae and B. oerstedtii are excluded from the genus Birisia as mismatching to the generic diagnosis. Species of Birisia are distinguished each other in size and degree of dissection of pinnules, in shape, presence and number of lobes, as well as the number of branches of the lateral veins inside the lobes. The pinnules of the Birisia are characterized by the significant variability and have a slightly different structure depending on their location on the leaf blade. Therefore, for a more accurate species identification of Birisia, it is necessary to have the most complete leaves with branching of two or three orders and the fertile pinnules.