Background and Aims The gymnosperm order Cycadales is pivotal to our understanding of seed-plant phylogeny because of its phylogenetic placement close to the root node of extant spermatophytes and its combination of both derived and plesiomorphic character states. Although widely considered a ‘living fossil’ group, extant cycads display a high degree of morphological and anatomical variation. We investigate stomatal development in Zamiaceae to evaluate variation within the order and homologies between cycads and other seed plants. Methods Leaflets of seven species across five genera representing all major clades of Zamiaceae were examined at various stages of development using light microscopy and confocal microscopy. Key Results All genera examined have lateral subsidiary cells of perigenous origin that differ from other pavement cells in mature leaflets and could have a role in stomatal physiology. Early epidermal patterning in a ‘quartet’ arrangement occurs in Ceratozamia, Zamia and Stangeria. Distal encircling cells, which are sclerified at maturity, are present in all genera except Bowenia, which shows relatively rapid elongation and differentiation of the pavement cells during leaflet development. Conclusions Stomatal structure and development in Zamiaceae highlights some traits that are plesiomorphic in seed plants, including the presence of perigenous encircling subsidiary cells, and reveals a clear difference between the developmental trajectories of cycads and Bennettitales. Our study also shows an unexpected degree of variation among subclades in the family, potentially linked to differences in leaflet development and suggesting convergent evolution in cycads.

中文翻译：

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苏铁科 Zamiaceae 的气孔发育

背景和目的 裸子植物苏铁目是我们理解种子植物系统发育的关键，因为它的系统发育位置靠近现存精子植物的根节点，并且它结合了衍生和拟态特征状态。尽管被广泛认为是“活化石”组，但现存的苏铁植物表现出高度的形态和解剖变异。我们调查了 Zamiaceae 的气孔发育，以评估苏铁和其他种子植物之间的顺序和同源性的变化。方法 使用光学显微镜和共聚焦显微镜在不同发育阶段检查代表 Zamiaceae 所有主要进化枝的 5 个属的 7 个物种的传单。主要结果 所检查的所有属都具有与成熟小叶中的其他铺面细胞不同的外源侧副细胞，并且可能在气孔生理学中起作用。“四重奏”排列的早期表皮图案发生在 Ceratozamia、Zamia 和 Stangeria。远端环绕细胞在成熟时硬化，存在于所有属中，除了 Bowenia，它在小叶发育过程中表现出相对较快的铺面细胞伸长和分化。结论 Zamiaceae 的气孔结构和发育突出了种子植物的一些同形性状，包括存在周围环绕的附属细胞，并揭示了苏铁和 Bennettitales 的发育轨迹之间的明显差异。