Reconstruction of a bennettitalean flower from the Carnian (Upper Triassic) of Lunz, Lower Austria

Abstract

The Bennettitales are a Mesozoic group of gymnosperms with complex reproductive organs that figure prominently in hypotheses on the ancestry and origin of angiosperms. However, the exact phylogenetic position of the Bennettitales is still debated, due in part to the scarcity of conclusive fertile remains from the Triassic. In this study we reconstruct a bennettitalean flower from isolated parts from the Carnian (Upper Triassic) of Lunz in Lower Austria, including Cycadolepis wettsteinii scale leaves, Haitingeria krasseri pollen organs, and Bennetticarpus wettsteinii ovulate organs/seed cones, based on correspondences in gross morphology and epidermal anatomy. The flower has small pollen organs with spreading and well-exposed pollen sacs; pollen sacs are not organised in synangia, and the ovulate organ is characterised by a low number of relatively large seeds and a large number of interseminal scales in relation to ovules/seeds. The flower lacks several of the characteristic features seen in geologically younger bennettitaleans, including fused, inwardly curved pollen organs and large number of small seeds. The association of these isolated organs to a single flower provides a rare opportunity to assess the attribution of these early representative of the Bennettitales, and sheds new light on the evolutionary history and phylogenetic position of this ancient group of seed plants.