Reproduction of Crassula helmsii by seed in western Europe

Bram D'hondt, Luc Denys, Wim Jambon, Roeland De Wilde, Tim Adriaens, Jo Packet, Johan van Valkenburg

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    The amphibious plant species Crassula helmsii is a widely established and still-spreading alien in various parts of Europe, where it is considered invasive as its dense swards stress the viability of local biota. The species was considered to exclusively reproduce through vegetative means, until
    ex situ germination was recorded from a single locality in Belgium. We assessed whether this seed viability holds on a wider scale, by testing 16 populations from The Netherlands, Belgium, northern France, eastern England and northern Germany in a greenhouse germination experiment. Seedlings were observed from all populations but two, and from each of the five countries. Although most fruits were lacking seeds and the inferred germination percentages were overall low, germinable seed numbers are considerable given the high density of flowering stems. An in situ test revealed seeds to make it through normal winter conditions without signs of physical damage and with retention of germinability. Our results suggest that reproduction by seed is a relatively cryptic but widespread phenomenon throughout western Europe. The persistency of seed banks requires further investigation. Nonetheless, these findings already challenge the efficacy of techniques currently applied in C. helmsii control.
    Original languageEnglish
    JournalAquatic Invasions
    Issue number2
    Pages (from-to)125–130
    Publication statusPublished - 2016

    Thematic List 2020

    • Water
    • Invasive species

    Thematic list

    • Flora
    • Invasive species (nature management)
    • Invasive species (management)
    • Invasive species (species diversity)

    EWI Biomedical sciences

    • B004-botany
    • B003-ecology

    Taxonomic list

    • higher plants (Plantae)
    • Crassulaceae


    • species directed nature management

    Free keywords

    • invasive alien species
    • invasive species


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