The Globally Rare Aldrovanda vesiculosa (Droseraceae) New to New Hampshire, U.S.A.

Aldrovanda vesiculosa L. (Droseraceae), the waterwheel plant, is a globally rare submerged aquatic carnivorous plant with extraordinarily fast-closing snap-traps and a highly specific suite of ecological requirements (Cross 2012). Plants are perennial, freefloating, and rootless, with linear, sparsely branched stems bearing whorls of 4–9 leaves terminated by bristles and a solitary, bi-lobed trap. The species is fast growing under optimal conditions and reproduction is predominantly clonal through the detachment of branches during favorable summer conditions (Adamec 1999). Plants overwinter by forming vegetative dormant turions at their apices in autumn. This stenotopic species usually grows in shallow, standing, dystrophic waters (Adamec 2018). The species is native to Europe, Africa, Asia, and Australia yet, due to recent rapid habitat degradation and population decline, nearly 90% of its historic occurrences are extinct, leaving only 50 natural sites remaining worldwide (Cross 2012). This critically endangered plant, with its novel aquatic carnivorous habit, has long been venerated by carnivorous plant hobbyists. Consequently, plants have been propagated and successfully introduced into many waterbodies in countries where it is not native. Deliberate introductions (or so-called assisted migration/colonization events) have become a more recent conservation tool for Aldrovanda vesiculosa (Adamec 2005; Cross 2012). About 30 artificial sites are known in Europe, Asia, and North America. Introductions (from Japanese sources) into the eastern United States first established the species in Virginia, and then subsequently into New Jersey and New York (Lamont et al. 2013). We report here on an assisted colonization effort, via a known carnivorous plant hobbyist, that led to an established population of Aldrovanda vesiculosa var. vesiculosa in southern New Hampshire. This represents the first documented occurrence of the species in New England and is its most northern station in North America. Plants of Japanese origin were deposited by the aforementioned hobbyist into a waterbody in Pelham, New Hampshire, in ca. 2010 in the hopes of establishing another locality for this imperiled species. The initial visit to the New Hampshire site in July 2017 confirmed the population survived, but in summer 2018 plants were not located. Plants were again observed in 2019 (Matthew Charpentier, Oxbow Associates Inc., pers. comm.). Annual