The abrupt origin and rapid diversification of the flowering plants during the Cretaceous has long been considered an “abominable mystery.” While the cause of their high diversity has been attributed largely to coevolution with pollinators and herbivores, their ability to outcompete the previously dominant ferns and gymnosperms has been the subject of many hypotheses. Common among these is that the angiosperms alone developed leaves with smaller, more numerous stomata and more highly branching venation networks that enable higher rates of transpiration, photosynthesis, and growth. Yet, how angiosperms pack their leaves with smaller, more abundant stomata and more veins is unknown but linked—we show—to simple biophysical constraints on cell size. Only angiosperm lineages underwent rapid genome downsizing during the early Cretaceous period, which facilitated the reductions in cell size necessary to pack more veins and stomata into their leaves, effectively bringing actual primary productivity closer to its maximum potential. Thus, the angiosperms' heightened competitive abilities are due in no small part to genome downsizing.

长久以来，白垩纪时期开花植物的突然起源和迅速多样化一直被认为是“令人难以置信的谜团”。尽管其高度多样性的原因在很大程度上归因于与传粉媒介和食草动物的共同进化，但它们胜过先前占主导地位的蕨类和裸子植物的能力却成为许多假设的主题。其中常见的是仅被子植物发育的叶片具有较小，较多的气孔和较高分支的脉络网络，从而能够提高蒸腾，光合作用和生长的速度。然而，被子植物如何用更小，更丰富的气孔和更多的静脉来包裹叶子是未知的，但与我们对细胞大小的简单生物物理限制有关。在白垩纪早期，只有被子植物谱系的基因组迅速缩小，这有助于减少将更多的静脉和气孔堆积到其叶子中所需的细胞大小，有效地使实际初级生产力接近其最大潜力。因此，被子植物增强的竞争能力在很大程度上要归功于基因组的缩小。