The inflated bladderwort (Utricularia inflata, Lentibulariaceae) is a submersed freshwater macrophyte that has recently expanded its range in the northeastern United States. To evaluate the potential and actual spread of this plant, we experimentally tested the ability of small (1.0 and 5.0 cm) stem fragments without apical meristems to survive and grow, and of 10 cm apices to grow at different pH levels. We also sampled vegetation in seven lakes to document the quantitative importance of U. inflata, and qualitatively surveyed 29 additional sites for its presence.
All fragments of both lengths survived, and produced new branches at similar rates (t-test: P = 0.62). Contrary to expectation, relative growth rates were 15% greater at pH 5 than pH 7 (P < 0.001), indicating that low pH per se does not limit this plant. Utricularia inflata has become an important component of the vegetation at greater depth in two of the seven lakes, and now occurs in 15 water bodies in three New York counties (Franklin, Hamilton, and Herkimer) - more than doubling the known locations for this invasive species. Current patterns of distribution strongly suggest that dispersal of U. inflata has occurred by downstream flow along chains of lakes, but also by boat traffic and/or waterfowl to account for its spread to new river drainages.