A phylogenomic analysis and revised infrageneric classification of Thesium (Santalaceae)

------------------------------------------------------------------------------------------ A phylogenomic analysis and revised infrageneric classification of Thesium (Santalaceae) ------------------------------------------------------------------------------------------ Natasha Lombard Foundational Biodiversity Science Division, National Herbarium, South African National Biodiversity Institute, Private Bag X101, Pretoria 0001, South Africa Department of Botany and Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa [e-mail] Félix Forest Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, United Kingdom [e-mail] Olivier Maurin Meise Botanic Garden, Meise, 1860 Belgium Fédération Wallonie-Bruxelles, Service Général de l’Enseignement supérieur & de la Recherche scientifique, Bruxelles, 1080 Belgium Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, United Kingdom [e-mail] M. Marianne le Roux Foundational Biodiversity Science Division, National Herbarium, South African National Biodiversity Institute, Private Bag X101, Pretoria 0001, South Africa Department of Botany and Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa [e-mail] Marge Poma, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, United Kingdom Abigail Carruthers Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, United Kingdom Ben-Erik van Wyk Department of Botany and Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa [e-mail] ------------------------------------------------------------------------------------------ AUTHOR CONTRIBUTIONS BVW, FF, MLR and NL designed the study. BVW, FF, MLR, NL and OM sourced samples, AC and MAPA conducted lab work, and OM data analyses. FF, MLR, NL and OM interpreted the results. NL wrote most the manuscript, with input from BVW, FF, MLR and OM and all authors provided comments. ------------------------------------------------------------------------------------------ ABSTRACT A phylogenomic analysis and revised infrageneric classification of Thesium (Santalaceae) is presented based on targeted enrichment using the Angiosperms353 probe set. This first targeted sequencing study includes 138 samples representing 106 species (approximately 32% of the genus). Our results provide substantially improved resolution compared to previous studies that utilized only a few gene regions, with an almost fully supported backbone topology. Thesium (including Austroamericium, Chrysothesium, Kunkeliella, and Thesidium) is confirmed as monophyletic and sister to a clade containing Lacomucinaea and Osyridicarpos. We recognize six monophyletic subgenera with full or strong support: T. subg. Hagnothesium, T. subg. Thesium, T. subg. Spinosa (newly described), T. subg. Discothesium (with revised circumscription), T. subg. Frisea, and T. subg. Psilothesium. We found T. subg. Discothesium as previously delineated to be paraphyletic and described a new subgenus, T. subg. Spinosa, to ensure monophyly of all subgenera. We formally recognised 18 sections in Thesium, of which nine are newly described and two are raised from lower ranks. Our phylogenetic clades show a strong biogeographic signal and despite sporadic morphological synapomorphies, most subgenera and sections can be distinguished by of combination of their distribution and morphology. We provide the first genetic evidence of potential hybridization in Thesium paving the way for further exploration of this long-hypothesised compounding factor. This study provides a robust framework for future taxonomic, biogeographic, and evolutionary studies of this diverse and problematic genus. ------------------------------------------------------------------------------------------ KEYWORDS Angiosperms353, hemiparasites, hybridization, Thesiaceae, Santalales, systematics ------------------------------------------------------------------------------------------