Effects of initial propagule size and water depth on Butomus umbellatus L. growth and vegetative propagation

Over the last century, flowering rush (Butomus umbellatus L.: Butomaceae) has escaped its native Eurasian range and has become a problematic species in parts of North America. As an aquatic invasive species, flowering rush has degraded wetlands in introduced areas and has interfered with human water usage. Although experimental work has been published regarding the reproductive biology of the species, we found few manipulative experiments aimed at testing ecological attributes of this species in the literature. The research reported here demonstrates that flowering rush is capable of aggressive clonal growth and propagation, whether from vegetative rhizome buds or from fragments of rhizomes themselves. This species was capable of growth along a depth gradient from zero to 132 cm and showed an ability to adjust biomass allocation along that gradient; however, biomass and asexual propagule production declined at depths beyond approximately 50 cm. The combination of regrowth from relatively small propagules, ability to tolerate depths of greater than one meter, and plasticity of biomass allocation along habitat gradients make this species a potential threat in many aquatic and wetland habitats in its introduced range. However, certain aspects of its biomass allocation strategies may enhance chemical control for plants growing at greater depths or those regenerating from rhizome buds, both of which tend to have greater S:R biomass ratios.