A new species of the freshwater fern Azolla (Azollaceae) from the Eocene Arctic Ocean

A new fossil species of the freshwater fern Azolla (Azollaceae, Salviniales) is described from an unusual setting of high palaeolatitude in the Arctic Ocean. Azolla arctica sp. nov., (lower Middle Eocene, Lomonosov Ridge) is represented by fully developed megaspore apparatuses with attached microspore massulae and clustered and dispersed microspore massulae. These abundant co-occurring fossils, combined with their associated biota, demonstrate that Azolla was growing and reproducing on a freshwater surface of the Eocene Arctic Ocean. Azolla arctica is compared with other fossil Azolla species, especially those from around Arctic and Nordic Seas. It documents new characteristics for the genus. The megaspore apparatus is small with a thin megaspore wall and a distinctive exoperine where nodular exoperinal masses fuse at several levels resulting in a rugulate, undulating, punctate to foveolate exoperine surface. Microspore massulae have two size classes of glochidia, short (< 25 µm) and long (> 55 µm), the anchor-shaped tips lack recurved flukes. These distinctive characters provide the potential to recognise Azolla arctica as fragmentary remains in palynological preparations from drill cores. Therefore, future comparisons with other fossils will reveal if a single species grew across the Arctic Ocean and if freshwater spills from the Arctic spread into the Nordic Seas.