Azolla mexicana C.Presl
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Plants seldom fruiting, a little larger than no. 1 [Azolla caroliniana Willd.], mostly 10–15 mm wide, ± pinnately branched when well developed, dichotomous only at the periphery; upper lf-lobes 0.7–0.9 mm, not much smaller than the lower, ± strongly imbricate; microsporocarps mostly a little over 1 mm thick; massulae 0.2–0.3 mm; glochidia with several cross-walls; megaspores 0.4–0.5 mm, the rounded base strongly pitted. Floating in still water; widespread in w. U.S., s. to n. S. Amer., and e. to Wis., Ill., and Ark. Rare.