PREMISE Undoubtedly, fossils are critical for understanding evolutionary transformations in deep time. Here, we reinvestigate the microspores and megaspores of Paleoazolla patagonica, a water fern found in Late Cretaceous sediments of the Chubut Province, Patagonia, Argentina, which provides novel evidence on the past history of the water fern clade. The study was based on recently collected specimens and additional observations of the original material. METHODS Most specimens analyzed herein were obtained from new palynological samples collected at the Cerro Bosta and Cañadón del Irupé localities, La Colonia Formation. Samples were mechanically disaggregated and treated with hydrofluoric and hydrochloric acid. Spores were studied using standard light microscopy and scanning electron microscopy. We also reexamined the original materials. RESULTS The newly described characters of Paleoazolla include the presence of heterosporangiate sori composed of one ellipsoidal megasporangium surrounded by three to four oval microsporangia, megasporangium containing one hairy massula that encloses two trilete megaspores (rarely one or three), and microsporangia containing numerous microspore massulae with non-septate multibarbed glochidia and one trilete microspore per massula. CONCLUSIONS The reinterpretation has revealed a novel set of characters for understanding the evolution of heterosporous water ferns. The presence of two megaspores in the megasporangium of Paleoazolla exposes serious gaps in the current knowledge on the evolution of monomegaspory in heterosporous water ferns, a fact that emphasizes the need of including fossils within phylogenies to elucidate patterns of character acquisition among water ferns.

中文翻译：

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重新解释Paleoazolla：来自阿根廷巴塔哥尼亚晚白垩世的杂孢水蕨

前提 毫无疑问，化石对于理解深层进化转变至关重要。在这里，我们重新研究了 Paleoazolla patagonica 的小孢子和大孢子，这是一种在阿根廷巴塔哥尼亚丘布特省晚白垩世沉积物中发现的水蕨，这为水蕨进化枝的过去历史提供了新的证据。该研究基于最近收集的标本和对原始材料的额外观察。方法 本文分析的大多数标本来自在 Cerro Bosta 和 Cañadón del Irupé 地区、La Colonia Formation 收集的新孢粉学样本。将样品机械分解并用氢氟酸和盐酸处理。使用标准光学显微镜和扫描电子显微镜研究孢子。我们还重新检查了原始材料。结果 Paleoazolla 新描述的特征包括存在由 1 个椭圆形大孢子囊组成的异孢子囊，由 3-4 个椭圆形小孢子囊包围，大孢子囊包含一个毛状团块，包围着 2 个三列大孢子（很少有 1 个或 3 个），小孢子囊包含多个小孢子团无分隔的多刺钩体和一个三列小孢子每个massula。结论 重新解释揭示了一组用于理解异孢水蕨进化的新特征。Paleoazolla 的大孢子囊中存在两个大孢子，这暴露了目前关于异孢水蕨中单大孢子进化的知识存在严重差距，