Format: ORAL

Kasper P. Hendriks1,2, Ihsan A. Al-Shehbaz3, Dmitry A. German4, C. Donovan Bailey5, Andreas Franzke6, Christiane Kiefer7, Marit Kuijt1, Marcus A. Koch6, Martin A. Lysak8, Sander van Zon1, Alexandre R. Zuntini9, Klaus Mummenhoff2, Frederic Lens1

1 Functional Traits, Naturalis Biodiversity Center, Leiden, The Netherlands 2 Department of Biology, Botany, University of Osnabrück, Osnabrück, Germany 3 Missouri Botanical Garden, St. Louis, USA 4 South-Siberian Botanical Garden, Altai State University, Barnaul, Russia 5 Department of Biology, New Mexico State University, Las Cruces, USA 6 Heidelberg Botanic Garden, Heidelberg University, Heidelberg, Germany 7 Centre for Organismal Studies (COS), Heidelberg University, Heidelberg, Germany 8 CEITEC–Central European Institute of Technology, Masaryk University, Brno, Czech Republic 9 Royal Botanic Gardens, Kew, Richmond, UK

Flowering plants are characterized by a great variation in woody and non-woody (i.e., herbaceous) growth forms. The first flowering plants were woody, but many lineages evolved into herbaceous species. Interestingly, roughly 700 lineages turned back towards a state of phylogenetically derived woodiness. This remarkable case of massive convergent evolution has baffled scientists since Darwin. Recent studies suggest drought as a main driving force, leading to a drought hypothesis. We study the mustard family (Brassicaceae; ~4,000 species), which alone represents one out of seven of all woodiness shifts in flowering plants, making it the perfect model family to understand woodiness evolution. We recently developed a protocol to sequence >1,000 nuclear genes from herbarium specimens, allowing the reconstruction of a robust, time-calibrated Brassicaceae Tree of Life (BrassiToL). This phylogenetic framework will be essential to identify all ~100 woodiness shifts, thereby generating a powerful framework to test for an evolutionary link between woodiness and the environment. Here, we present our initial results, including a robust BrassiToL of over half the family’s species, with a focus towards 'woody tribes' like Anastaticeae, Heliophileae, and Lepidieae. Our first analyses of woodiness evolution suggest that drought is correlated with woodiness in at least several of the family’s tribes, including Brassiceae and Alysseae. However, we found other factors to also correlate with woodiness, including UV intensity (Arabideae, Brassiceae, Thelypodieae) and aseasonality (Alysseae, Descurainieae, Erysimeae). In the face of global warming and periods of prolonged drought, understanding how plants cope with drought is essential, warranting a thorough assessment of the drought hypothesis.