TY - JOUR T1 - Organogenesis and Vasculature of <em>Anaxagorea</em> Revealing the Axial Homologs in the Carpel and its Implications for the Origin of Angiosperms JF - bioRxiv DO - 10.1101/2020.05.22.111716 SP - 2020.05.22.111716 AU - Ya Li AU - Wei Du AU - Shuai Wang AU - Xiao-Fan Wang Y1 - 2020/01/01 UR - http://biorxiv.org/content/early/2020/05/26/2020.05.22.111716.abstract N2 - Background and Aims The carpel is the definitive structure of angiosperms, the origin of carpel is of great significance to the phylogenetic origin of angiosperms. Traditional view was that angiosperm carpels were derived from structures similar to macrosporophylls of pteridosperms or cycads, which bear ovules on the surfaces of foliar organs. In contrast, other views indicate that carpels are originated from the foliar appendage enclosing the ovular axis. One of the key differences between these two conflicting ideas lies in whether the “axial homologs” are involved in the evolution of carpel. The aim of this paper is to investigate whether the “axial homologs” remain in the carpel of extant angiosperms.Methods Anaxagorea was used for organogenesis and comparative anatomical study due to its outstanding and unusually long carpel stipe. The continuous change of vascular bundles at carpel stipe in different developmental stages was described in detail.Key Results Organogenesis study shows that the carpel stipe of Anaxagorea occurs at the early stage of carpel development. Vascular bundles at the base of Anaxagorea carpel are a set of discrete ring-arranged collateral bundles (RACBs), which branch out at the upper portion into two sets of RACBs below each ovule.Conclusions The ring-arranged collateral bundles indicates a clear morphological evidence for the existence of the “axial homologs” in the carpel and thus support the idea that carpels originated from the integration of the ovular axis and foliar parts. This finding may promote reconsiderations regarding the origin of the carpel and facilitate a greater understanding of the phylogenetic relationship between angiosperms, gnetophytes and Cordaitales.Competing Interest StatementThe authors have declared no competing interest. ER -