Publication: Enum. Filic. 273. 1824.
selected vouchers: WTU
Notes: KZ99 gives authorities as Schlecht. & Cham. ex K. Presl, here we follow H&C and FNA Vol. 2.
FNA2: "Azolla mexicana is generally less cold tolerant and has a narrower environmental range than A . caroliniana . Both species are closely related and are similar vegetatively in culture. In the western United States, A . mexicana is often fertile."