STEMS: glabrous. PLANT: 0.7–3.0 cm long, sometimes to 5 cm in cultivation (Fig. 3). FLOATING LEAF LOBES: 0.5–0.8 mm long, somewhat convex, usually with hyaline or reddish margins (turning entirely dull reddish brown in the autumn), the minute adaxial trichomes 1-celled. MEGASPORES with the hemispherical portion having irregularly confluent, angular papillae, sometimes appearing irregularly pitted, also sparsely to moderately tomentose with long, loosely curled trichomes; the collar somewhat concave, glabrous, the cap appearing fibrous. GLOCHIDIA: with an average of 3–5 crosswalls. 2n = 44, 66. NOTES: Ponds, lakes, and backwaters of rivers, in still or sluggish water, sometimes stranded on mud: Cochise, Coconino, Graham, Greenlee, La Paz, Maricopa, Mohave, Pima, Pinal, Santa Cruz cos. (Fig. 1; also reported, but not vouchered, from Yuma Co.); 600–1200 m (2000–4000 ft); WA to CA and AZ, w Can., Mex., s to S. Amer.; introduced in HI and the Old World.Populations of A. filiculoides in Arizona are uncommon and sporadic. Waterfowl move the plants around and eventually it may be discovered at other sites in the state. REFERENCES: G.Yatskievych and M.D. Windham, 2008, Vascular Plants of Arizona: Azollaceae. CANOTIA 4 (2): 31–34.