Azolla filiculoides
The species of Azolla are difficult to tell apart because the plants are small and the characters used to separate them are difficult to see, requiring the use of a light microscope to see epidermal hairs and a scanning electron microscope for examination of megaspores. Moreover, most of the plants collected are sterile and lack the megaspores needed for identification. The genus is important in the cultivation of rice because all species can fix atmospheric nitrogen, thus resulting in greater crop yields. Several species have been brought into Hawai'i for horticultural and experimental purposes (Lumpkin 1993) .
Azolla filiculoides Lamarck was deliberately brought into the Islands as part of a mosquito abatement program in rice fields, but it was not until around 1934 that it became fully naturalized in taro patches and irrigation ditches on O'ahu (Fosberg 1943) . In 1950 Wagner reported that he had collections of it from both O'ahu and Maui. It is now well established in flooded areas on all the islands except Hawai'i, where it most likely also occurs, although I have seen no collections. Azolla filiculoides can be found floating in flooded areas such as taro patches, rice paddies, ditches, and ponds. It can form large mats that can prevent weed growth and thereby reduce mosquito breeding.
Azolla caroliniana Willdenow has recently been identified as being established in Hawai'i, but confirmation of its identity is needed.
The occurrence of Azolla filiculoides on the island of Hawai'i was documented in 1999 by a collection made from a taro farm in the Waipio Valley (Imada 99-16, BISH).
