Reproduction of Crassula helmsii by seed in Western Europe
Crassula helmsii (EPPO A2 List: Crassulaceae) is an amphibious succulent perennial species native to temperate Australia and New Zealand. The species forms extensive monospecific mats in wetlands throughout Western Europe enabling C. helmsii to outcompete native species for space, light and nutrients. In Europe C. helmsii readily reproduces through vegetative regeneration of turions and stem fragments. Flowering occurs in most populations between July and September, though the ability of the species to reproduce through seed in Europe remains largely unknown. In the present study, the reproductive ability of C. helmsii was evaluated by assessing if (1) seeds are present in populations from across Western Europe, (2) whether the seeds are viable and (3) whether the seeds can survive until the next growing season. Plant material containing flowers and fruits was collected during the autumn of 2014 from 16 populations in the Netherlands, Belgium, France, England and Germany. Following a period of cold stratification, seed viability was tested from each population. Seedlings were grown from seed samples from all populations except two, and from all of the five countries. The results of an in situ test revealed that seeds can survive under normal winter conditions. The results suggest that reproduction by seed is a relatively cryptic but widespread phenomenon throughout Western Europe and that these findings can have implications on the efficacy of management techniques currently applied for the control of C. helmsii.
D’hondt B, Denys L, Jambon W, De Wilde, Adriaens T, Packet J, van Valkenburg J (2016) Reproduction of Crassula helmsii by seed in western Europe. Aquatic Invasions. http://www.aquaticinvasions.net/2015/ACCEPTED/AI_2016_Dhondt_etal_correctedproof.pdf