The ovule and its developmental successor, the seed, together represent a highly characteristic feature of seed plants that has strongly enhanced the reproductive and dispersal potential of this diverse group of taxa. Ovules encompass multiple tissues that perform various roles within a highly constrained space, requiring a complex cascade of genes that generate localized cell proliferation and programmed cell death during different developmental stages. Many heritable morphological differences among lineages reflect relative displacement of these tissues, but others, such as the second (outer) integuments of angiosperms and Gnetales, represent novel and apparently profound and independent innovations. Recent studies, mostly on model taxa, have considerably enhanced our understanding of gene expression in the ovule. However, understanding its evolutionary history requires a comparative and phylogenetic approach that is problematic when comparing extant angiosperms not only with phylogenetically distant extant gymnosperms but also with taxa known only from fossils. This paper reviews ovule characters across a phylogenetically broad range of seed plants in a dynamic developmental context. It discusses both well-established and recent theories of ovule and seed evolution and highlights potential gaps in comparative data that will usefully enhance our understanding of evolutionary transitions and developmental mechanisms.

中文翻译：

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种子植物胚珠的进化和模式

胚珠及其发育继承者种子共同代表了种子植物的一个高度特征，它极大地增强了这一多样化分类群的繁殖和传播潜力。胚珠包含多种组织，在高度受限的空间内发挥各种作用，需要复杂的基因级联，在不同的发育阶段产生局部细胞增殖和程序性细胞死亡。谱系之间的许多可遗传的形态差异反映了这些组织的相对位移，但其他的，如被子植物和 Gnetales 的第二（外）珠被，代表了新颖的、显然是深刻的和独立的创新。最近的研究，主要是关于模型分类群，大大增强了我们对胚珠中基因表达的理解。然而，了解它的进化历史需要一种比较和系统发育的方法，当将现存的被子植物不仅与系统发育上遥远的现存裸子植物，而且与仅从化石中已知的分类群进行比较时，这是有问题的。本文回顾了动态发育环境中系统发育范围广泛的种子植物的胚珠特征。它讨论了成熟的和最近的胚珠和种子进化理论，并强调了比较数据中的潜在差距，这些差距将有助于增强我们对进化转变和发育机制的理解。本文回顾了动态发育环境中系统发育范围广泛的种子植物的胚珠特征。它讨论了成熟的和最近的胚珠和种子进化理论，并强调了比较数据中的潜在差距，这些差距将有助于增强我们对进化转变和发育机制的理解。本文回顾了动态发育环境中系统发育范围广泛的种子植物的胚珠特征。它讨论了成熟的和最近的胚珠和种子进化理论，并强调了比较数据中的潜在差距，这些差距将有助于增强我们对进化转变和发育机制的理解。