In the Palaeogene, pollen assemblages at low and mid latitudes are characterized by abundant palm and palm-like (PPL) taxa. Although these taxa have been widely reported, their occurrence in the Palaeogene of Myanmar remains poorly documented. Here we report on the morphology of PPL pollen along a middle to upper Eocene sedimentary sequence in central Myanmar and discuss their nearest living relatives (NLRs). Principal components analysis (PCA) indicates that Palmaepollenites kutchensis, Dicolpopollis and Longapertites were dispersed from freshwater plants, whereas the parent taxon of Proxapertites operculatus was probably a member of the coastal vegetation in the manner of Spinizonocolpites. This, with sedimentological data, suggests a palaeoenvironmental change from a brackish, tidally influenced environment to a fully freshwater setting through the late Eocene. Additionally, we mapped and compared the geographical distribution of selected Eocene palm taxa and their NLRs, and found that their distributions shrank after the Eocene. Moreover, in the Palaeogene, species diversity of selected PPL taxa seems lower in Myanmar than in the Indian subcontinent and other regions in South-East Asia. We hypothesize that in the Eocene the Indo–Asian collision zone formed a ‘hotspot’ for palm diversity, which is reflected in species-rich palynofloras. However, the local palm diversity declined after the Eocene, whereas, at the global level, palm distribution was distinctly reduced between the Eocene and the present. We propose that the retreat of the palms may have occurred as early as the Eocene – Oligocene Transition (EOT), but this remains to be confirmed by the study of EOT pollen records in tropical regions.

中文翻译：

---

从东南亚和全球角度看缅甸中部始新世棕榈树：来自孢粉学记录的证据

在古近纪，低纬度和中纬度的花粉组合以丰富的棕榈和棕榈状 (PPL) 类群为特征。尽管这些分类群已被广泛报道，但它们在缅甸古近纪的出现仍然鲜有记载。在这里，我们报告了缅甸中部沿始新世中上层沉积序列的 PPL 花粉形态，并讨论了它们最近的生活亲属 (NLR)。主成分分析 (PCA) 表明 Palmaepollenites kutchensis、Dicolpopollis 和 Longapertites 分散于淡水植物中，而 Proxapertites operculatus 的亲本分类群可能以 Spinizonocolpites 的方式属于沿海植被。这与沉积学数据表明，从微咸水、通过晚始新世，受潮汐影响的环境变为完全淡水环境。此外，我们绘制并比较了选定的始新世棕榈类群及其 NLR 的地理分布，发现它们的分布在始新世之后缩小。此外，在古近纪，缅甸选定的 PPL 类群的物种多样性似乎低于印度次大陆和东南亚其他地区。我们假设在始新世印亚碰撞区形成了棕榈多样性的“热点”，这反映在物种丰富的孢粉植物群中。然而，始新世之后当地棕榈多样性下降，而在全球范围内，始新世和现在之间的棕榈分布明显减少。我们认为棕榈树的退缩可能早在始新世-渐新世过渡期（EOT）就发生了，