The freshwater fern Azolla (Azollaceae) from Eocene Arctic and Nordic Sea sediments: New species and their stratigraphic distribution

• We describe 3 new Azolla species from Eocene marine deposits.
• In total 5 Azolla species occurred in the Arctic and Nordic Seas during the Eocene.
• Some species grew in situ on the surface of the ocean.
• Some species were washed into the sediments from nearby land.
• The stratigraphic distribution of all 5 Azolla species is discussed.

Three new species of the freshwater fern Azolla are described from Eocene marine deposits of the Arctic and Nordic seas, bringing the total number of species now documented from these areas to five. Azolla arctica Collinson et al., Azolla jutlandica Collinson et al., Azolla nova sp. nov. and Azolla nuda sp. nov. are known from both megaspore apparatuses and microspore massulae, and occur at more than one site. Their microspore massula characters are sufficiently distinctive to allow their recognition in palynological preparations. Presence or absence of hairs on the microspore massula surface and glochidia bases is shown to be a useful species diagnostic character and is worthy of greater attention in Azolla taxonomy. The fifth species, Azolla astroborealis sp. nov., is only known from a few megaspore apparatuses in the Northstar 1 Well in the western Arctic, but these are strikingly different from those of the other four species e.g., in having nine distinct pseudovacuolate floats.Samples from cores and most individual sites contain more than one Azolla species. This indicates that conditions were particularly favourable for growth of Azolla for a prolonged time interval in the latest early and possibly earliest middle Eocene (latest Ypresian and earliest Lutetian) around the western Arctic and the Norwegian–Greenland Sea.