PREMISE Fossils provide fundamental evidence of the evolutionary processes that crafted today's biodiversity and consequently for understanding life on Earth. We report the finding of Myrtaceidites eucalyptoides pollen grains preserved within the anthers of a 52-million-year-old Eucalyptus flower collected at Laguna del Hunco locality of Argentinean Patagonia and discuss its implications in understanding the evolutionary history of the iconic Australian genus Eucalyptus. METHODS Pollen grains were extracted from the flower's anthers and were then observed under light microscopy and scanning electron microscopy. The phylogenetic position of the fossil was investigated by adding pollen data to a previously published total-evidence matrix and analyzing it using parsimony. RESULTS We erect the species Eucalyptus xoshemium for the fossil flower. Pollen extracted from E. xoshemium belongs to the species Myrtaceidites eucalyptoides, which, until now, was only known as dispersed pollen. The numerous pollen grains recovered from the single flower allowed estimation of M. eucalyptoides' variability. Results of the phylogenetic analysis reinforce the position of this fossil within crown group Eucalyptus. CONCLUSIONS The discovery of these pollen grains within a Patagonian Eucalyptus fossil flower confirms the hypothesis that Myrtaceidites eucalyptoides represents fossil pollen in the Eucalyptus lineage, extends the geographic and stratigraphic fossil pollen record, and supports an earlier age for crown-group eucalypts.

中文翻译：

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5200万年前的桉树花脱落的数量比花粉粒还多


前提化石提供了进化过程的基本证据，这些进化过程塑造了今天的生物多样性，从而帮助我们了解地球上的生命。我们报告了在阿根廷巴塔哥尼亚 Laguna del Hunco 地区采集的一朵 5200 万年前桉树花的花药中保存的桃金娘桉树花粉粒的发现，并讨论了其对了解澳大利亚标志性桉树属进化历史的影响。方法从花的花药中提取花粉粒，然后在光学显微镜和扫描电子显微镜下观察。通过将花粉数据添加到先前发布的总证据矩阵中并使用简约法对其进行分析，研究了该化石的系统发育位置。结果我们建立了桉树品种作为花化石。从 E. xoshemium 中提取的花粉属于桃金娘属 eucalyptoides 物种，迄今为止，这种花粉仅被称为分散花粉。从单朵花中回收的大量花粉粒可以估计桉树的变异性。系统发育分析的结果强化了该化石在冠群桉树中的地位。结论 在巴塔哥尼亚桉树化石花中发现这些花粉粒证实了桃金娘桉树代表桉树谱系中花粉化石的假设，扩展了地理和地层化石花粉记录，并支持冠群桉树的更早年龄。