Evolution of polyploidy and apomixis in the pantropically distributed and species-rich genus Zanthoxylum (Rutaceae)

by Lee Ping Ang
Doctoral thesis
Date of Examination:2025-03-10
Date of issue:2025-04-22
Advisor:Prof. Dr. Elvira Hörandl
Referee:Prof. Dr. Alexander Schmidt
Referee:Prof. Dr. Elvira Hörandl
Persistent Address: http://dx.doi.org/10.53846/goediss-11183

 

 

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Abstract

English

The proto-Rutaceae group includes genera with significant economic and evolutionary importance, yet their phylogenetic relationships and evolutionary mechanisms remain incompletely understood. This thesis focuses on the evolutionary history of Zanthoxylum (prickly ash, Sichuan pepper) and one of its sister genera, Tetradium, addressing knowledge gaps through modern phylogenomic methods, including hybrid capture. For Tetradium, a genus of nine species distributed across Eastern and Southeastern Asia, hybrid capture data was used to resolve interspecific relationships and clarify taxonomic questions. Phylogenetic analyses revealed five main groups supported by molecular and morphological data, with ovule number and seed functionality emerging as key evolutionary traits. Taxonomic revisions include revising Euodia meliifolia var. celebica as Tetradium celebicum and reassigning two fossils, Euodia costata and Euodia lignata, to T. costatum and T. lignatum, respectively. A description for T. celebicum and an identification key for all species of Tetradium are provided. For Zanthoxylum, a pantropical genus of approximately 225 species, the hybrid capture method allowed a comprehensive phylogenetic analysis involving 453 specimens. The study resolved Zanthoxylum as monophyletic, identifying four main biogeographic clades and assessing the monophyly of key species. Zanthoxylum is monophyletic only if heterochlamydeous-flowered species are merged into it. Three out of five currently accepted sections proved to be monophyletic. Furthermore, one species, Z. fagara, is found to be polyphyletic while the remaining most species are monophyletic. Potential hybridization and incomplete lineage sorting were also detected, highlighting the need for future nomenclatural revisions. Finally, the thesis explores chromosome evolution and polyploidy within Zanthoxylum, by using flow cytometry and a bioinformatic approach - nQuire. Together, these studies provide high-resolution phylogenetic insights and evolutionary interpretations, enhancing our understanding of Tetradium and Zanthoxylum within the Rutaceae family and offering new molecular data for future evolutionary research.
Keywords: Hybrid capture, Rutaceae, Phylogenomics
 
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