Format: ORAL

Julius JEITER1,*, Maria-Anna VASILE2, Maximilian WEIGEND2

1 Chair of Botany, Faculty of Biology, TUD Dresden University of Technology, 01062 Dresden, Germany 2 Bonn Institute for Organismic Biology (BIOB), Plant Biodiversity Section, University of Bonn, Meckenheimer Allee 170, 53115 Bonn, Germany *email: julius.jeiter@tu-dresden.de

Boraginales constitute a medium-sized order in the Lamiids with a chequered taxonomic history due to considerable diversity in flower and fruit morphology. In recent decades, molecular phylogenetics established Boraginales as a well-defined order with two major clades. Both comprise families characterised by either capsules or nutlets and capsules, schizocarps and/or drupes. A reduction in ovule number from many to four appears to have preceded the transition from capsular to indehiscent fruits. We address two main questions: Why did indehiscent fruits derived from a bicarpellate, syncarpous gynoecium evolve twice independently? What are the main factors driving fruit evolution in Boraginales? We combine scanning electron microscopy and X-ray micro-computed tomography in the context of recent phylogenies to understand gynoecium and fruit morphological evolution within Boraginales. We focus on three examples from Boraginales II. Our studies of gynoecium and fruit morphology address patterns in ovule and seed number evolution. In Hydrophyllaceae we found multiple transitions from pluri-ovulate to four-seeded fruits, but reversals of this character are rare. We argue that the reduction of ovule number to four fixes an ontogenetic trajectory, ultimately leading to indehiscent, four-seeded fruits. Conversely, in holoparasitic Pholisma arenarium, parasitism has likely led to a departure from the two carpel-four ovule paradigm in Boraginales, resulting in a multiplication of carpels to increase seed number. Finally, in Heliotropiaceae, we found fruit architecture to be highly conserved and divergent fruit morphology and function is realized by histological changes. Multiple transitions between schizocarps and drupes occurred even within closely related taxa within the family. These morphological and developmental studies underscore the multiple ontogenetic trajectories available for morphological diversification and functional convergence, even where particular character combinations are highly conserved. Traditional Boraginales systematics have emphasised mature fruit morphology phylogenetic data clearly demonstrate that this often fails to reflect relationships correctly.