Wildenow 1810
Family: Azollaceae.
Synonyms: Azolla cristata Kaulfuss, Sal-vinia azolla Raddi, Azolla densa Desvaux, A. portoricensis Sprengel. Etymology: Azolla: from azo (Greek) = drought and ollyo = to kill, points to the dying off of the fern during drought periods; caroliniana: originating from Carolina (North America).
• Distribution: North, Central and South America, naturalized in Europe, two discovery cases in Asia.
Description: Aquatic plant, floating on the water surface or rooted in bog; 0.7-2.5 cm in size. Horizontal stem, hardly fork-branched. Alternate leaves, densely distichous and overlapping, scalous. Each leaf is divided into 2 lobes: the upper lobe is located above water and assimilates, is thick, 1.5 x 0.7-1.1 mm in size, almost acute, with a narrow, colorless margin, green or a deep red-brown coloration (autumn-colored), papilloes pubescent topside; pubescence 2-celled, water-repellent. The upper lobe features a cavity, opened downwards, in which the blue algae Ana-
- Azolla caroliniana.
baena azollae leads a symbiotic existence with Azolla. The lower lobe is dipped into the water and is thin and colorless.
Sporocarps are located on the lower lobe of older specimens. Microsporocarp (male, larger than the female) with 8-40 petiolate globular microsporangia which contain many spores, these in turn are joined to form 3-6 groups (massuli). Massuli covered with densely horizontally striped glochidiums (petiolate barbs which assist anchoring). Macro-sporangium with only macrospore. Chromosome number 2n = 48. Culture: Refer to Azolla filiculoides. Ecology: Azolla caroliniana is more rare in native waters than the larger A. filiculoides, which is mainly due to the moderate formation of spores and fruit, which are, however, essential for the development of new plants in spring. Both species love nutrient-rich water. Water analyses were conducted at two natural locations in Peru during July 1990: 1) Rio Nanay, little water movement, larger populations of A. caroliniana with Utricularia foli-osa, water temperature 25 °C, GH and KH < 1 °dH, pH 5.8, 10 |xS/cm; and 2) Rio Yana-yacu (Ucayali catchment area), bay with only little water movement, on the bank a thick layer of floating plants consisting of A. caroliniana, Ceratopteris pteridoides, Eichhornia crassipes, Limnobium laevigatum, Phyllan-thus fluitans, Pistia stratiotes, Ricciocarpus natans, Salvinia auriculata, Utricularia foli-osa. For a detailed water analysis see biotope No. 6 on p. 40.
Other: The blue algae Anabaena azollae, which exists in a symbiotic relationship with Azolla, is able to bind the air nitrogen. It is due to this that Azolla is used for fertilization of rice paddies. At the same time, the genus Azolla has a high nutritional value, and is therefore suitable as cattle and fish food. In some areas Azolla is utilized to prevent mosquito plagues. In India Azolla is served fried, and in Africa the plants are supposed to be a component in the manufacture of soap. In
New Zealand Azolla is used as a medicine against throat infection. Further reading: Lumpkin and Plucknett (1980).
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