Resolving intricate taxonomies by using type material, Hyb-Seq and geometric morphometrics. – A proof-of-concept from the nasty Xanthium L.. Xanthium_project

Taxonomy is an important cornerstone of systematic biology. Producing reliable taxonomies is particularly challenging in complexes in which morphological and/or genetic differentiation is not substantial among lineages. In these complexes, contradicting taxonomies have been often proposed and taxonomic names are recursively misapplied. The present project aims at setting up a conceptual workflow for delimiting coherent evolutionary lineages in intricate taxonomic groups, using herbarium material (including types), phylogenomics (Hyb-Seq) and geometric morphometrics, along with coalescent-based species delimitation approaches. The inclusion of name-bearing types in the analyses will tremendously facilitate taxonomic assessments, accelerating nomenclatural work.We are going to test the workflow on Xanthium, a morphologically intricate genus of the sunflower family. Several lineages of Xanthium nowadays have a cosmopolitan distribution, making impossible the completion of a comprehensive phylogenetic study based solely on field-collections. We are going to employ approximately 240 specimens (in a large part herbarium material), exhaustively covering the whole geographic distribution and morphological diversity registered in two intricate complexes of the genus (i.e., the X. orientale complex and X. spinosum s.l.). Genomic data will be gathered with Hyb-Seq techniques, using the "Asteraceae COS baits kit". Leaf shape and traits of the burs (i.e., the female capitula) will be used in geometric morphometric analyses. Using integrative approaches (capable of simultaneously analysing genetic and phenotypic data) we are going to delimit coherent evolutionary lineages. Finally, we will link lineages to taxonomic names, thanks to the inclusion of type material in the analyses. In collaboration with other projects of the SPP program, we will work towards a methodological synthesis of such workflows in very different taxonomic groups (such as plants and animals).