• How plant seeds originated remains unresolved, in part due to disconnects between fossil intermediates and developmental genetics in extant species. The Carboniferous fossil Genomosperma is considered among the most primitive known seeds, with highly lobed integument and exposed nucellus. We have used this key fossil taxon to investigate the evolutionary origins of seed development.
• We examined sectioned Genomosperma specimens using modern digital 3D reconstruction techniques and established population‐level measurements of Genomosperma ovules for quantitative analysis.
• Genomosperma ovules show significant variation in integumentary lobe fusion and curvature. Our analysis suggests that this variation represents a single species with significant variations in lobe number and fusion, reminiscent of floral development in extant species. We conclude that changes in lobe flexure occurred late in development, consistent with a previously hypothesized function in pollen guidance/retention. We also identify seeds of Genomosperma within cupules for the first time.
• The presence of a cupule adds evidence towards the plesiomorphy of cupules within seed plants. Together with the similarities identified between the Genomosperma lobed integument and floral organs, we propose that the cupule, integument and nucellus together developed in a shoot‐like fashion, potentially ancestral to extant seed plant reproductive shoots.

中文翻译：

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重建最早的种子外皮的发展为祖传种子结构的演变提出了新的假设。

• 植物种子如何起源仍未解决，部分原因是化石中间体与现存物种的发育遗传学之间脱节。石炭化石基因被子植物被认为是最原始的已知种子，具有高裂的外皮和裸露的核。我们已经使用了这个重要的化石分类单元来研究种子发育的进化起源。
• 我们使用现代的数字3D重建技术检查了切片的Genomosperma标本，并建立了Genomosperma胚珠的种群水平测量值以进行定量分析。
• 基因型精子胚珠在皮间融合和曲率上显示出显着变化。我们的分析表明，这种变异代表单个物种的叶数和融合显着变化，让人联想到现存物种的花期发育。我们得出的结论是，叶挠曲的变化发生在发育后期，这与先前假设的花粉引导/保留功能一致。我们还首次在吸盘中鉴定了Genomosperma的种子。
• 吸盘的存在为种子植物中吸盘的形变提供了证据。结合鉴定出的Genomosperma浅叶状外被膜和花器官之间的相似性，我们认为该小杯，外被膜和细胞核以芽样方式发育，可能起源于现存的种子植物生殖芽。