New records for Eastern Mosquito Fern (Azolla cristata, Salviniaceae) in Canada

We report a cluster of Eastern Mosquito Fern (Azolla cristata, Salviniaceae) populations in five watersheds within a 56-km2 area of Leeds and Grenville County, Ontario. Some of the recently discovered populations were immense, one containing over two million individuals in 2016. These eastern Ontario populations are persistent, having been observed in situ continuously for four years. One population was confirmed after an apparent absence of at least 30 years and another was reported as present (or at least recurring) for approximately 50 years. We observed that Canadian A. cristata is capable, at least experimentally, of overwinter dormancy and subsequent renewal. Azolla cristata in eastern Ontario and western Quebec appears to represent naturally (if sporadically) occurring populations, likely transported from adjacent northern New York populations by migratory waterfowl. These natural occurrences are expected to be more frequent as climate change continues to reduce environmental barriers to the northward establishment of this and other southern taxa