The red-orange coloration of the aquatic fern, Azolla, growing in the sun is well documented (Benedict, 1923; Moore, 1969; Olsen, 1970). However, the pigments that contribute to this coloration are not known to have been identified. Harborne (1965) has identified a number of anthocyanins (3-deoxyanthocyanidins) found in the ferns Adiantum, Dryopteris, and Pteris. The purposes of this paper are to report on the identification of the anthocyanins in Azolla mexicana Presl and to describe the environmental factors which may influence this coloration. On 15 and 28 July 1975, I collected specimens ofA. mexicana Presl from a pond in southwestern Jackson County, Illinois. Some specimens were identified by W. Carl Taylor and me by their sporocarps, and regular and SEM photographs were made. Others of the collection were washed of epiphytes, blotted dry of excess water, and placed directly into a solution of 1% HC1 in methanol. The extracted pigments were separated by one dimensional paper chromatography employing three solvent systems [BAW (n-butanol: glacial acetic acid: water, 4:1:5, top layer), 1% HC1 in water, and Forestal (acetic acid: conc. HC1: water, 15:3:82)] on Whatman #1 chromatography paper (Harbore, 1967). Pigment spots were identified by visible and UV radiation and by comparing Rf values and coloration with those of published reports (Harbore, 1967). Tentatively identified anthocyanin spots were then cut out and extracted in 1% HCI in methanol and the resultant extract assayed with a Beckman DBGT Spectrophotometer to determine peak wavelength and height ratio.