Photo by Quite Adept licensed under CC BY-NC-ND 2.0
Say the words "flowering rush" and many will picture some grass-like, pond vegetation. However, the plant I am talking about today is not a rush at all. Known scientifically as Butomus umbellatus, the flowering rush superficially resembles a patch of true rushes, especially when not in flower. However, it is actually quite a unique species and the sole member of the family Butomaceae. Native to parts of Europe and Asia, this beautiful aquatic plant can now be found invading wetlands throughout northern North America.
Growing quite tall and producing an umbel of beautiful pink flowers, it is no wonder that this plant came to North America as a horticultural curiosity. Its overall appearance suggests a relationship with the genus Allium but genetic analysis puts it somewhere near the water plantains - Alismataceae. The interesting thing about this plant is that here in North America, individual populations exhibit either diploid or triploid chromosome counts.
Photo by Christian Fischer licensed under CC BY-SA 3.0
This is most likely a function of its horticultural past. Many commonly grown garden species have been selected for polyploidy in their chromosomes. Polyploid plants are often larger and more hardy than their diploid relatives, mostly due to the extra genetic material they harbor. It has been noted that there seems to be some reproductive differences between diploid and triploid flowering rush populations as a result. Diploids are more likely to reproduce sexually via seeds whereas triploids are usually sterile and reproduce vegetatively. Triploids are also less commonly found as escapees but they are more widely distributed than diploids. This is likely due to the fact that triploids are more commonly planted in gardens.
Whereas it seems that there is plenty of areas where people disagree on the invasive species issue, one thing we must keep in mind is that, no matter where you stand, biological invasions are one of the largest natural experiments this world has ever seen. We mustn't waste any opportunity to learn from these invasions and to gather as much data as we possibly can. Species like flowering rush offer us insights into how and why some species become invasive while others do not. The more we know, the better we can learn from the mistakes of the past.