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Grimsson, Friogeir; Grimm, Guido W.; Potts, Alastair J.; Zetter, Reinhard; Renner, Susanne S. (2018): A Winteraceae pollen tetrad from the early Paleocene of western Greenland, and the fossil record of Winteraceae in Laurasia and Gondwana. In: Journal of Biogeography, Vol. 45, No. 3: pp. 567-581
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Abstract

Aim: Winteraceae comprise c.130 species in seven genera, with the greatest species diversity in the Pacific (Pseudowintera, Zygogynum), Australia (Bubbia, Tasmannia), New Guinea (Belliolum, Bubbia, Zygogynum, Tasmannia) and Madagascar (Takhtajania). Only Drimys occurs in South America. Because of their Cretaceous leaves, wood and pollen fossils, and their lack of xylem vessels, Winteraceae throw light on early angiosperm evolution. We describe a Winteraceae pollen tetrad from the Paleocene of Greenland, review the family's fossil record and palaeogeography and document its current climate preferences. Location: Worldwide. Methods: Extant and fossil pollen were studied with light and scanning electron microscopy. Molecular phylogenetic and character mapping approaches were used to infer the evolution of pollen characters, and 37,842 collections from the Global Biodiversity Information Facility were used to infer the climate and vegetation types occupied by today's Winteraceae and to compare them to the Paleocene climate and vegetation of Greenland as inferred from the fossil record of other families. Results: Winteraceae are the only flowering plants with persistent, acalymmate tetrads composed of ulcerate grains with a distinct reticulate sculpturing. The tetrad described here as Pseudowinterapollis agatdalensis Grimsson & Zetter spec. nov. comes from Agatdalen valley in western Greenland and dates to the Early Paleocene, Danian, 64-62Ma. It shows the complete character suite of modern Winteraceae and overlaps the LM characters of the three previously known Pseudowinterapollis species from Australia, New Zealand and South Africa. The palaeoflora of the Agatdal Formation consisted of a mixed deciduous-evergreen forest resembling habitats where Winteraceae occur today. Main conclusions: Macro- and microfossil records of Winteraceae extend back to the Upper Cretaceous in both Laurasia and Gondwana, and the family's biogeography, like that of its sister family, Canellaceae, cannot be understood by focusing only on southern Gondwana. Winteraceae instead were part of broadleaved forests in Paleocene and Eocene North American and Greenland and may have reached Europe via the North Atlantic Land Bridge, explaining Eocene Winteraceae wood in northern Germany.