Data_Sheet_2_A flat petal as ancestral state for Ranunculaceae.pdf

Ranunculaceae comprise ca. 2,500 species (ca. 55 genera) that display a broad range of floral diversity, particularly at the level of the perianth. Petals, when present, are often referred to as “elaborate” because they have a complex morphology. In addition, the petals usually produce and store nectar, which gives them a crucial functional role in the interaction with pollinators. Its morphological diversity and species richness make this family a particularly suitable model group for studying the evolution of complex morphologies. Our aims are (1) to reconstruct the ancestral form of the petal and evolutionary stages at the scale of Ranunculaceae, (2) to test the hypothesis that there are morphogenetic regions on the petal that are common to all species and that interspecific morphological diversity may be due to differences in the relative proportions of these regions during development. We scored and analyzed traits (descriptors) that characterize in detail the complexity of mature petal morphology in 32 genera. Furthermore, we described petal development using high resolution X-Ray computed tomography (HRX-CT) in six species with contrasting petal forms (Ficaria verna, Helleborus orientalis, Staphisagria picta, Aconitum napellus, Nigella damascena, Aquilegia vulgaris). Ancestral state reconstruction was performed using a robust and dated phylogeny of the family, allowing us to produce new hypotheses for petal evolution in Ranunculaceae. Our results suggest a flat ancestral petal with a short claw for the entire family and for the ancestors of all tribes except Adonideae. The elaborate petals that are present in different lineages have evolved independently, and similar morphologies are the result of convergent evolution.

毛茛科（Ranunculaceae）约包含2500个物种、55个属，展现出广泛的花部多样性，尤以花被（perianth）层面最为突出。若存在花瓣，则其常被称为「特化花瓣」，因形态结构极为复杂。此外，花瓣通常会产生并储存花蜜，这使其在与传粉者的互作中发挥关键功能。
该科的形态多样性与物种丰富度，使其成为研究复杂形态演化的理想模式类群。
本研究的目标有二：其一，在毛茛科的整体尺度下重建花瓣的祖先形态与演化阶段；其二，验证下述假说：花瓣上存在所有物种共有的形态发生区域，而物种间的形态多样性或源于这些区域在发育过程中相对比例的差异。
我们对32个属的成熟花瓣形态复杂性进行了性状（描述子）评分与分析。此外，我们借助高分辨率X射线计算机断层扫描（HRX-CT），对6种花瓣形态迥异的物种（Ficaria verna、Helleborus orientalis、Staphisagria picta、Aconitum napellus、Nigella damascena、Aquilegia vulgaris）的花瓣发育过程进行了详细描述。
本研究基于该科一套可靠且带有时间校准的系统发育树开展祖先状态重建，据此为毛茛科的花瓣演化提出了全新假说。
研究结果显示，整个毛茛科以及除侧金盏花族（Adonideae）外所有族的祖先花瓣，均为具短爪的扁平花瓣。不同演化支中出现的特化花瓣均为独立演化而来，相似的形态结构实则源于趋同演化。