Asexual Reproduction and its Potential Influence on the Distribution of an Invasive Macrophyte

Utricularia inflata (Swollen Bladderwort) is a submersed macrophyte that is expanding its range in the northeastern US. Although Swollen Bladderwort is a new addition to this region, Utricularia purpurea (Purple Bladderwort) and U. vulgaris (Common Bladderwort) are 2 morphologically similar free-floating species within the invaded waterways. Through a series of greenhouse and field studies, we sought to distinguish traits among these 3 macrophytes. We conducted a greenhouse experiment to compare the vegetative propagation of Swollen Bladderwort and Common Bladderwort in a temperature-controlled tank. In field trials, we examined the displacement of all 3 species by water movement and their distribution across a range of depths at 5 lake sites. Swollen Bladderwort and Common Bladderwort both produced potential propagules, but exhibited differences in their asexual reproduction. New Common Bladderwort branches grew significantly longer, while Swollen Bladderwort fragments exhibited a greater number of new branches. Each new branch has the potential to develop into a new individual as the original stolon decays; this trait may help explain how Swollen Bladderwort is quickly establishing populations in newly colonized lakes. The results of the displacement experiment showed that all species were less likely to remain in the shallows compared to deeper waters. However, displacement of Swollen Bladderwort was greater than Common Bladderwort. Vegetation sampling also indicated that Common Bladderwort and bladderwort species attached to the sediment (U. resupinata [Lavender Bladderwort] and U. intermedia [Flat-leaf Bladderwort]) are found in the shallows, while Swollen Bladderwort and Purple Bladderwort are found at greater depths. These results suggest that Swollen Bladderwort is more susceptible to water movement and may be spread to downstream systems at a faster rate, compared to Common Bladderwort and attached bladderwort species.