The Albian fern flora of Alexander Island, Antarctica

• Alexander Island macrofossils from the Antarctic Peninsula represent a diverse plant community.
• Within the flora, ferns are the most diverse component, and here we describe 11 of the 24 fern taxa, erecting two new genera.
• Ferns were diverse and ecologically dominant, despite the presence of early angiosperms.
• In the Antarctica, ferns were diverse in the Jurassic and Early Cretaceous, but subsequently declined in diversity.

The Albian Alexander Island macrofossil flora from the Antarctic Peninsula preserves a diverse community of liverworts (Marchantiophyta), ferns (Polypodiopsida), Lycopodiales, Equisetales, Cycadales, Ginkgoales, seed-ferns (Bennettitales and Pentoxylales), Coniferales, and the first representatives of angiospermous leaves in Antarctica. Despite the presence of angiosperms in this assemblage, ferns are the most diverse element of the flora and are also ecologically dominant, while angiosperms contribute a smaller component to floristic diversity and have low abundance. Here we describe 11 fern taxa from this assemblage. The fossils are assigned to Cladophlebis, Sphenopteris and two newly created genera. The new genera and species are described under Adiantitophyllum serratum gen. et. sp. nov. and Nunatakia alexanderensis gen. et. sp. nov., and the new species are recognized as Cladophlebis dissecta sp. nov., Cladophlebis drinnanii sp. nov., Cladophlebis macloughlinii sp. nov. and Sphenopteris sinuosa sp. nov. In total, there are 24 fern species known from Alexander Island. In comparison to older floras (Jurassic) there is a greater diversity of ferns, while latest Cretaceous floras preserve significantly fewer fern species and more angiosperms. Possible factors that might account for such high fern diversity are high rainfall or generally humid conditions, regular disturbances by flooding and occasionally fire, and the preservation of a diverse range of fern communities that represent several palaeoenvironments.