September 2013. An invasive weed was found in New Caledonia, presumably in drains or ditches.

It was identified as the floating aquatic fern Azolla (Family Salviniaceae – formerly Azollaceae), although the resolution of the images isn’t particularly good. In Australia there are two species, Azolla filiculoides and Azolla pinnata. One way of differentiating between the two species is whether fine rootlets are present along the main roots (Azolla pinnata). I do not have any information on which species are present in New Caledonia although Queensland Herbarium has at least one record of Azolla pinnatafrom Noumea. According to Mabberley (2006 – 3^rd edition) there are 5 species worldwide. Azolla filiculoides is sometimes called “Pacific Azolla”.

The sender said that both A. filiculoidesand A. pinnata are present in New Caledonia: http://idtools.org/id/aquariumplants/Aquarium_&_Pond_Plants_of_the_World/key/Aquarium_&_Pond_Plants/Media/Html/Fact_sheets/azolla.html

There is a useful US-based online key to aquatic weeds (with an app version in the pipeline). The Azolla entry can be seen here – http://idtools.org/id/aquariumplants/Aquarium_&_Pond_Plants_of_the_World/key/Aquarium_&_Pond_Plants/Media/Html/Fact_sheets/azolla.htm.