Germination of Crassula helmsii seed in Europe
Crassula helmsii (Crassulaceae EPPO A2 List) is a semi-aquatic plant species which can grow in a number of forms (submerged, emergent or semi-terrestrial) depending on environmental conditions. The species is native to Australia and New Zealand and has been introduced into the EPPO region as an oxygenating plant for aquaria and ponds. C. helmsii reproduces vegetatively. Seed formation has been confirmed from populations in Belgium, France, the Netherlands and the United Kingdom. However, it is not clear what role sexual reproduction plays in the ecology of the species.
Seed viability was tested in germination trials using plant material collected from ten populations in Belgium. Seeds were sown on agar and germination was recorded. In a comparative trial, wilted flowers from the same populations (assumed to contain mature seeds) were sown in a soil substrate, with germination estimated based on the number of seeds per flower. C. helmsii populations exhibited high germination rates, with an estimated overall mean of 68.5 %. The flower-based trial yielded lower germination (13.8 %). The results show that C. helmsii populations in Belgium produce numerous viable seeds that germinate readily and have the potential to form a seedbank. These results can have important implications for the management of this invasive species.
Sources
D’hondt B, Brutsaert S, Dermout W, Neukermans A, Packet J, Adriaens T (2026) Seed germination trials of the invasive plant Crassula helmsii from nature restoration sites in Belgium. Plant Ecology and Evolution, 159, 536-545.