A fertile pinnule fragment with spores of Dicksonia from Early Oligocene sediments in Tasmania

Abstract

A new fern species, Dicksonia dissecta (Dicksoniaceae), is described from Early Oligocene sediments at Little Rapid River, western Tasmania, based on a fertile frond fragment containing sporangia and spores. The frond morphology is distinct from all extant species of Dicksoniaceae, but the sori indicate that the fossil is Dicksonia. The spores have affinity with those of the extant tropical and subtropical Australian species, D. youngiae and D. herbertii and with dispersed fossil spores with a more or less continuous record in southeastern Australia from the late Paleocene to the Early Pleistocene. Dicksonia dissecta represents the first fossil record of sculptured in-situ spores of Dicksoniaceae. Unsculptured spores assigned to Matonisporites ornamentalis and M. cooksoniae are common in Cainozoic sediments in Australia, and probably represent a lineage of Dicksonia distinct from that of D. dissecta.