Latin.filix, fern, + -ulus, diminutive suffix, +-aides, like, resembling; the plant is a little fern.
Stems branching pinnately, alternately, bearing threadlike roots. Fronds overlap-ping, 1.5-5 cm long. Pinnae overlapping, 2-lobed, 0.5-1.5 mm long, the upper lobes oblong-ovate, yellowish green, pink, or dark red, upper side convex, underside deeply con-cave, lower (submerged) lobes larger, pale green to whitish, delicately membranous, glabrous.
Widespread in low-elevation taro patches, irrigation ditches, and ponds on all major islands.
Native to the United States, western Canada, Mexico, and Central and South America and purposely brought to Hawai 'i as part of a mosquito control program in rice fields early in the twentieth century. By 1934 A. filiculoides had become fully naturalized. The ability of its blue-green alga symbiont to fix nitrogen makes it a source of fertilizer.
Azolla filiculoides is a small, flat fern found as floating patches in stagnant, slow-moving waters such as taro patches, rice paddies, ditches, and ponds. It is easily sep-arated from Salvinia by its smaller fronds and the presence of threadlike roots (com-pared with the rootlike submerged leaves of Salvinia ).