BACKGROUND Quantification of corolla shape variations helps biologists to investigate plant diversity and evolution. 3D images capture the genuine structure and provide comprehensive spatial information. RESULTS This study applied X-ray micro-computed tomography (µCT) to acquire 3D structures of the corollas of clade Corytholoma and extracted a set of 415 3D landmarks from each specimen. By applying the geometric morphometrics (GM) to the landmarks, the first 4 principal components (PCs) in the 3D shape and 3D form analyses, respectively, accounted for 87.86% and 96.34% of the total variance. The centroid sizes of the corollas only accounted for 5.46% of the corolla shape variation, suggesting that the evolutionary allometry was weak. The 4 morphological traits corresponding to the 4 shape PCs were defined as tube curvature, lobe area, tube dilation, and lobe recurvation. Tube curvature and tube dilation were strongly associated with the pollination type and contained phylogenetic signals in clade Corytholoma. The landmarks were further used to reconstruct corolla shapes at the ancestral states. CONCLUSIONS With the integration of µCT imaging into GM, the proposed approach boosted the precision in quantifying corolla traits and improved the understanding of the morphological traits corresponding to the pollination type, impact of size on shape variation, and evolution of corolla shape in clade Corytholoma.

中文翻译：

---

表型变异、进化异速生长和花冠形状的祖先状态的 3D 揭示：Corytholoma 分支（苦苣苔科 Ligeriinae 亚族）的案例研究。


背景花冠形状变化的量化有助于生物学家研究植物多样性和进化。 3D 图像捕捉真实结构并提供全面的空间信息。结果本研究应用 X 射线微计算机断层扫描 (μCT) 获取冠冕分支花冠的 3D 结构，并从每个标本中提取一组 415 个 3D 标志。通过对地标应用几何形态计量学 (GM)，3D 形状和 3D 形状分析中的前 4 个主成分 (PC) 分别占总方差的 87.86% 和 96.34%。花冠质心大小仅占花冠形状变异的5.46%，表明进化异速生长较弱。对应于 4 种形状 PC 的 4 种形态特征被定义为管曲率、叶面积、管扩张和叶反曲。管曲率和管扩张与授粉类型密切相关，并包含冠状分支中的系统发育信号。这些地标进一步用于重建祖先状态的花冠形状。结论 通过将μCT成像集成到GM中，所提出的方法提高了量化花冠性状的精度，并增进了对与授粉类型相对应的形态性状、尺寸对形状变异的影响以及花冠形状进化的理解。