Biodiversity and Plant systematics Dr. Nora Walden

Different aspects of phylogenetics and the evolutionary history of the Brassicaceae (mustard family) have been the main focus of my research over the past years. More recently, I have also been fascinated by understanding complex and reticulate evolutionary histories across different timescales, from recent hybridization and polyploidization to deep evolutionary divergence. The Brassicaceae family, with high numbers of recent polyploids and frequent hybridization, offer a great model system to investigate phylogenetic discordance and its potential causes (hybridization, polyploidization, incomplete lineage sorting) and consequences. In addition to phylogenomics, I also use comparative genomics methods and synteny analyses to study the evolution of genes in the context of entire chromosomes. Much of my work has also focused on the evolutionary history of the genus Arabidopsis and on North American Arabidopsis lyrata, mostly using population level sampling and population genetic methods.

Phylogenomics of Arabideae

With around 4000 species in 350 genera, the Brassicaceae are among the most species rich angiosperm families. Over ten percent of Brassicaceae taxa belong to the tribe Arabideae, which among others contains the species rich genera Arabis and Draba. Polyploidization, posing a particular challenge to phylogenetic reconstruction, is common among Arabideae species, and ploidy levels of octaploid and higher are not uncommon in Draba. Using target enrichment data, we reconstruct a robust phylogenetic hypothesis which serves as an anchor for further analyses of morphological evolution through space and time and to study (parallel) evolution of traits.

Conservation genetics of Nuphar

Nuphar pumila (Nymphaceae) is an aquatic plant with a mostly northern/arctic distribution (Scandinavia, Russia). Populations in Central and Western Europa are regarded as glacial relicts and are threatened by habitat loss through anthropogenic impact as well as introgression from Nuphar lutea, a closely related species. Using ddRAD sequencing we investigate status of introgression and develop molecular markers to monitor the advancement of hybridization for nature conservation.

The evolutionary history of Cardamine bulbifera

Cardamine bulbifera (Brassicaceae) is a dodecaploid species exclusively propagating through bulb-like structures. Despite its seemingly complete absence of sexual reproduction, the species was able to colonize large parts of Europe postglacially. We study the evolutionary history and adaptive potential of this plant using genomic datasets.

Recent speciation of Cochlearia excelsa

Cochlearia excelsa (Brassicaceae) is a highly endangered, cold-adapted small range endemic from the Eastern Alps. It likely diverged from its closest relative, Cochlearia pyrenaica, during the Pleistocene. We use population genomic methods to investigate the dynamics of divergence and gene flow between both species.

Courses in BSc Biowissenschaften / BSc Biologie 50% 

• Evolution der Landpflanzen 
  Microscopy-centered course offered in the winter semester; can be combined with additional modules as part of the Praktikum Pflanzen im Lebensraum.
• Grundlagen der Bioinformatik 
  Winter semester course that may be integrated into the Methodische Grundlagen der Evolutionsbiologie practical module.
• Bestimmungsübungen Pflanzen – Intensivkurs 
  Intensive plant identification course that can be combined with other modules within Praktikum Pflanzen im Lebensraum II.

• PhD in Biology, Heidelberg University, 2016 – summa cum laude

• Postdoctoral Researcher, Universität Basel, 2016–2018 – with Prof. Yvonne Willi 

  Plant Ecology and Evolution | Department of Environmental Sciences | University of Basel

• Postdoctoral Researcher, Heidelberg University, 2019

• Guest Researcher, Wageningen University, 2019–2022 – DFG fellowship (HO 6443/1) in the group of Prof. Eric Schranz 

  Biosystematics Group - WUR

• Since May 2022: Scientific Staff, Biodiversity & Plant Systematics, Centre for Organismal Studies, Heidelberg University

Walden, N., Koch, M.A. (2025). Genetic signatures of long-term evolutionary success in a herbaceous, high-polyploid, clonal plant species in Central European woodlands. Annals of Botany. mcaf298. https://doi.org/10.1093/aob/mcaf298.

Walden, N., Mansion, G., Schnorf, H., Koch, M.A., Guggisberg, A. (2025). Murbeckiella is dead, long live Oreophyton - Origin and systematics of Tribe Oreophytoneae (Brassicaceae). Annals of Botany. mcaf115. https://doi.org/10.1093/aob/mcaf115.

Kiefer M., German D.A., Kiefer C., Hendriks K.P., Franzke A., Schmickl R., Walden N., BrassiTEN, Koch M.A. (2025) Capacity building in crucifer research – from BrassiBase to a taxonomic expert network (BrassiTEN). Plant Systematics and Evolution 310: e30.

Thomas, S.K., Abrahams, R.S., Kick, D., Walden, N., Conant, G., McKain, M., An, H., Arias, T., Edger, P., Harkess, A., Hendriks, K., Koch, M.A., Lens, F., Lysak, M., McAlvay, A., Mummenhoff, K., Al-Shehbaz, I., Washburn, J., Pires, J.C. (2025). Polylpoidy as a taxonomic clade marker for mustard crops and relatives. Annals of Botany. mcaf170. https://doi.org/10.1093/aob/mcaf170.

Hoang, N.V., Walden, N., Caracciolo, L., Luoni, S.B., Retta, M., Li, R., Wolters, F.C., Woldu, T., Becker, F.F.M., Verbaarschot, P., … Schranz, M.E. (2024). Expanding the Triangle of U: Comparative analysis of the Hirschfeldia incana genome provides insights into chromosomal evolution, phylogenomics and high photosynthesis-related traits. Annals of Botany. mcae179. https://doi.org/10.1093/aob/mcae179.

Walden, N., Kiefer, C., and Koch, M.A. (2024). Unravelling complex hybrid and polyploid evolutionary relationships using phylogenetic placement of paralogs from target enrichment data. https://doi.org/10.1101/2024.06.28.601132.

Lucek, K., Giménez, M.D., Joron, M., Rafajlović, M., Searle, J.B., Walden, N., Westram, A.M., and Faria, R. (2023). The Impact of Chromosomal Rearrangements in Speciation: From Micro- to Macroevolution. Cold Spring Harbor Perspectives in Biology. 2023:15(11). https://doi.org/10.1101/cshperspect.a041447.

Hendriks, K.P., Kiefer, C., Al-Shehbaz, I.A., Bailey, C.D., Hooft van Huysduynen, A., Nikolov, L.A., Nauheimer, L., Zuntini, A.R., German, D.A., Franzke, A., Koch, M.A., Lysak, M.A., Toro-Núñez, Ó., Özüdoğru, B., Invernón, V.R., Walden, N., Maurin, O., Hay, N.M., Shushkov, P., … Lens, F. (2022). Global Brassicaceae phylogeny based on filtering of 1,000-gene dataset. Curr. Biol. 33: 4052–4068.

Hoang, N.V., Sogbohossou, E.O.D., Xiong, W., Simpson, C.J.C., Singh, P., Walden, N., van den Bergh, E., Becker, F.M., Li, Z., Zhu., X.-G., Bräutigam, A., Weber, A.P.M., van Haarst, J.C., Schijlen, E., Hendre, P.S., van Deynze, A., Achigan-Dako, E.G., Hibberd, J.M. and Schranz, E.M. (2023). The genome of Gynandropsis gynandra provides insights into whole-genome duplications and the evolution of C4 photosynthesis in Cleomaceae. Plant Cell 35: 1334–1359.

Walden, N., & Schranz, M. E. (2022). Synteny identifies reliable orthologs for phylogenomics and comparative genomics of the Brassicaceae. Genome Biology and Evolution 15 (3), evad034.

Willi, Y., Lucek, K., Bachmann, O. and Walden, N. (2022). Recent speciation associated with range expansion and a shift to self-fertilization in North American Arabidopsis. Nat. Commun. 13:7564.

Fulgione, A., Neto, C., Elfarargi, A., Tergemina, E., Ansari, S., Göktay, M., Dinis, H., Döring, N., Flood, P., Rodriguez-Pacheco, S., Walden, N., Koch, M.A., Roux, F., Hermisson, J. and Hancock, A. (2022). Parallel reduction in flowering time from de novo mutations enable evolutionary rescue in colonizing lineages. Nat. Commun. 13: 1461.

Patsiou, T., Walden, N., and Willi, Y. (2021). What drives species’ distributions along elevational gradients? Macroecological and -evolutionary insights from Brassicaceae of the central Alps. Glob. Ecol. Biogeogr.: geb.13280.

Walden, N., German, D.A., Wolf, E.M., Kiefer, M., Rigault, P., Huang, X.-C., Kiefer, C., Schmickl, R., Franzke, A., Neuffer, B., Mummenhoff, K., and Koch, M.A. (2020). Nested whole-genome duplications coincide with diversification and high morphological disparity in Brassicaceae. Nat. Commun. 11: 3795.

Walden, N., Lucek, K., and Willi, Y. (2020). Lineage-specific adaptation to climate involves flowering time in North American Arabidopsis lyrata. Mol. Ecol.: mec.15338. 

Walden, N., Nguyen, T.-P., Mandáková, T., Lysak, M.A., and Schranz, M.E. (2020). Genomic blocks in Aethionema arabicum support Arabideae as next diverging clade in Brassicaceae. Front. Plant Sci. 11: 719.

Lucek, K., Galli, A., Gurten, S., Hohmann, N., Maccagni, A., Patsiou, T., and Willi, Y. (2019). Metabarcoding of honey to assess differences in plant-pollinator interactions between urban and non-urban sites. Apidologie 50: 317–329.

Lucek, K., Hohmann, N., and Willi, Y. (2019). Postglacial ecotype formation under outcrossing and self-fertilization in Arabidopsis lyrata. Mol. Ecol. 28: 1043–1055.

Hohmann, N., Wolf, E.M., Rigault, P., Zhou, W., Kiefer, M., Zhao, Y., Fu, C.-X., and Koch, M.A. (2018). Ginkgo biloba’s footprint of dynamic Pleistocene history dates back only 390,000 years ago. BMC Genomics 19.

Novikova, P.Y., Hohmann, N., and Van de Peer, Y. (2018). Polyploid Arabidopsis species originated around recent glaciation maxima. Curr. Opin. Plant Biol. 42: 8–15.

Hohmann, N. and Koch, M.A. (2017). An Arabidopsis introgression zone studied at high spatio-temporal resolution: interglacial and multiple genetic contact exemplified using whole nuclear and plastid genomes. BMC Genomics 18.

Novikova P.Y., Hohmann N., Nizhynska V., Tsuchimatsu T., Ali J., Muir G., Guggisberg A., Paape T., Schmid K., Fedorenko O.M., et al. (2016). Sequencing of the genus Arabidopsis identifies a complex history of nonbifurcating speciation and abundant trans-specific polymorphism. Nat. Genet. 48: 1077–1082.

Jacquemin, J., Hohmann, N., Buti, M., Selvaggi, A., Müller, T., Koch, M.A., and Schmid, K.J. (2016). Levels and patterns of genetic diversity differ between two closely related endemic Arabidopsis species. bioRxiv 048785; doi: https://doi.org/10.1101/048785.

Hohmann, N., Wolf, E.M., Lysak, M.A., and Koch, M.A. (2015). A time-calibrated road map of Brassicaceae species radiation and evolutionary history. Plant Cell 27: 2770–2784.

Muir, G., Ruiz-Duarte, P., Hohmann, N., Mable, B.K., Novikova, P., Schmickl, R., Guggisberg, A., and Koch, M.A. (2015). Exogenous selection rather than cytonuclear incompatibilities shapes asymmetrical fitness of reciprocal Arabidopsis hybrids. Ecol. Evol. 5: 1734–1745.

Hohmann, N., Schmickl, R., Chiang, T.-Y., Lučanová, M., Kolář, F., Marhold, K., and Koch, M.A. (2014). Taming the wild: resolving the gene pools of non-model Arabidopsis lineages. BMC Evol. Biol. 14: 224.

Koch, M.A., Scheriau, C., Betzin, A., Hohmann, N., and Sharbel, T.F. (2013). Evolution of cryptic gene pools in Hypericum perforatum: the influence of reproductive system and gene flow. Ann. Bot. 111: 1083–1094.

Yang, C., Bratzel, F., Hohmann, N., Koch, M., Turck, F., and Calonje, M. (2013). VAL- and AtBMI1-mediated H2Aub initiate the switch from embryonic to postgerminative growth in Arabidopsis. Curr. Biol. 23: 1324–1329. 

Wörz, A., Hohmann, N., and Thiv, M. (2012). Morphological and molecular diversity of some populations of Gagea (Liliaceae) in Southwest Germany. Stuttg. Beitr. zur Naturkunde A: 11.