TY - JOUR T1 - Organogenesis and Vasculature of <em>Anaxagorea</em> and its Implications in the Integrated Axial-Foliar Origin of the Angiosperm Carpel 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/2020/07/01/2020.05.22.111716.abstract N2 - The carpel is the definitive structure of angiosperms and the origin of the carpel is of great significance to the phylogenetic origin of angiosperms. The traditional view has been that angiosperm carpels emerged from structures similar to macrosporophylls of pteridosperms or Bennettitales, which bear ovules on the surface of foliar organs. Conversely, according to other perspectives, carpels originated from foliar appendages enclosing the ovule-bearing axis. One of the key distinctions between the two conflicting views lies in whether the ovular axis is involved in the evolution of the carpel. The aim of the present study was to investigate whether the axial homologs remain in the carpel of extant angiosperms, and, in turn, reveal the integrated axial-foliar nature of carpel. Two Anaxagorea species were used for organogenesis and comparative anatomical studies owing to their outstanding and unusually long carpel stipes. The continuous change of vascular bundles at the carpel stipe at different developmental stages is described here in detail. Organogenesis revealed that the carpel stipe of Anaxagorea emerges at the early stage of carpel development. Vascular bundles at the base of Anaxagorea carpel are a set of discrete ring-arranged collateral bundles that branch out at the upper portion into two sets of ring-arranged collateral bundles below each ovule. The ring-arranged collateral bundles are clear morphological evidence of the existence of axial homologs in the carpel, and, therefore, support the perspective that carpels originated from the integration of the ovular axis and foliar parts. This finding could prompt the reconsideration of how the bract-bracteole-terminal ovule system in gymnosperms evolved into an angiosperm carpel.Competing Interest StatementThe authors have declared no competing interest. ER -