Odd ploidy-level cytotypes in sexually reproducing species are considered a dead end due to absent or reduced fertility. If sterility is only partial, however, their contribution to the population gene pool can be augmented by longevity and clonal growth. To test this, we investigated the cytotype origin and spatial pattern, and pollen viability in three relict shrub species of the genus Daphne (Thymelaeaceae Juss.) in central Europe. Daphne cneorum subsp. cneorum is a widespread European species that has a broad ecological amplitude, whereas D. cneorum subsp. arbusculoides and D. arbuscula are narrow endemics of the western Pannonian Plain and the Western Carpathians, respectively. Our study confirmed that all three taxa are diploid. However, of more than a thousand analysed individuals of D. cneorum subsp. cneorum, five in four different populations were triploid. Our data indicate that these triploids most likely originate from recurrent autopolyploidization events caused by the fusion of reduced and unreduced gametes. High pollen viability was observed in all three taxa and in both diploid and triploid cytotypes, ranging from 65 to 100 %. Our study highlights the significant role of odd ploidy-level cytotypes in interploidy gene flow, calling for more research into their reproduction, genetic variability, and overall fitness. Interestingly, while the endemic D. arbuscula differs from D. cneorum based on genetic and genome size data, D. cneorum subsp. arbusculoides was indistinguishable from D. cneorum subsp. cneorum. However, our study reveals that the subspecies differ in the number of flowers per inflorescence. This is the first comprehensive cytogeographic study of this intriguing genus at a regional scale, and in spite of its karyological stability, it contributes to our understanding of genomic evolution in plant species with a wide ecological amplitude.

Botanical Garden of Pavol Jozef Šafárik University in Košice Mánesova 23 SK 043 52 Košice Slovak Republic

Department of Biology and Ecology Faculty of Natural Sciences Matej Bel University in Banská Bystrica Tajovského 40 SK 974 01 Banská Bystrica Slovak Republic

Department of Biology and General Ecology Faculty of Ecology and Environmental Sciences Technical University in Zvolen Ul T G Masaryka 24 SK 960 01 Zvolen Slovak Republic

Department of Botany Faculty of Science Charles University Benátská 2 CZ 128 01 Praha Czech Republic

Department of Evolution and Systematics Institute of Botany Plant Sciences and Biodiversity Centre Slovak Academy of Sciences Dúbravská cesta 9 SK 845 23 Bratislava Slovak Republic

Department of Forest Ecology Czech University of Life Sciences Prague CZ 16 521 Suchdol Praha 6 Czech Republic

Department of Taxonomy and Evolution Institute of Biological Research 48 Republicii St R 400015 Cluj Napoca Romania

Faculty of Biology University of Bucharest Splaiul Independenței 91 95 R 050095Bucharest Romania

Institute of Biology and Ecology Faculty of Science Pavol Jozef Šafárik University in Košice Mánesova 23 SK 041 54 Košice Slovak Republic

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