Elucidating the origin of carpel has been a challenge in botany for long time. The Unifying Theory suggested that the carpel originate from a composite organ comprising an ovule-bearing shoot and a foliar part enclosing the shoot. A logical inference from this theory is that placenta in angiosperms should have radiosymmetrical vasculature, just like that in a young branch. Anaxagorea is the most basal genus of the primitive angiosperm family, Annonaceae. The conspicuous carpel stipe makes it an ideal material for exploring the carpel vasculature. In this study, serial sections of flower and carpel were delineated in Anaxagorea luzonensis and A. javanica, and a three-dimensional model of the carpel vasculature was reconstructed. The results show that (1) vascular bundles at both the carpel stipe and the ovule/placenta are in a radiosymmetrical pattern, (2) the amphicribral bundles would develop into ring-arranged bundle complex with the carpel maturation, (3) the ovule/placenta bundles were separated from the bundles of the carpel wall, and, (4) all the radiosymmetrical vasculature (including amphicribral bundles and ring-arranged bundle complexes) in the carpel were fed by a larger radiosymmetrical bundle system. These results suggest that the radiosymmetrical pattern of carpel vasculature are in line with the Unifying Theory.

中文翻译：

---

环状排列的血管图案是茎唯一的吗？Anaxagorea（Annonaceae）心皮脉管系统的三维重建及其进化意义

长期以来，阐明心皮的起源一直是植物学中的挑战。统一理论认为，心皮起源于复合器官，该复合器官包括带有胚珠的芽和包围芽的叶面部分。该理论的逻辑推论是，被子植物中的胎盘应该具有放射对称的脉管系统，就像年轻的分支一样。Anaxagorea是原始被子植物Annonaceae的最基础的属。明显的心皮柄使其成为探索心皮脉管系统的理想材料。在这项研究中，花和心皮的连续切片被描绘在Anaxagorea luzonensis和A. javanica中，并且重建了心皮脉管系统的三维模型。结果表明：（1）心皮柄和胚珠/胎盘处的血管束呈放射线对称性；（2）两栖束带会随着心皮成熟而发展成环状排列的束复合体；（3）胚珠/胎盘束与心皮壁束分开，并且，（4）心皮中所有不对称的脉管系统（包括两肋束和成环排列的束复合体）由较大的不对称束系统供食。这些结果表明，心皮血管的放射线对称性与统一理论相符。（4）心皮中所有不对称的脉管系统（包括两肋束和成环排列的束复合物）均由较大的不对称束系统供食。这些结果表明，心皮血管的放射线对称性与统一理论相符。（4）心皮中所有不对称的脉管系统（包括两肋束和成环排列的束复合物）均由较大的不对称束系统供食。这些结果表明，心皮血管的放射线对称性与统一理论相符。