Azolla

  • Authority

    Mickel, John T. & Beitel, Joseph M. 1988. Pteridophyte Flora of Oaxaca, Mexico. Mem. New York Bot. Gard. 46: 1-580.

  • Family

    Salviniaceae

  • Scientific Name

    Azolla

  • Description

    Genus Description - Plants minute, free-floating or on mud; stems slender, branching, with unbranched roots and two rows of imbricate leaves; leaves bilobed, with an upper green lobe and colorless lower lobe, cavities in the leaves containing a nitrogen-fixing blue-green alga, Anabaena azollae; heterosporous; sporangia in nutlike unisexual sporocarps, globose microsporocarp with numerous microsporangia, megaspo-rocarp with single megasporangium containing a single megaspore, the microspores in four clumps (massulae) per sporangium with distinctive, anchor-shaped glochidia, the megaspores with flotation lobes.

  • Discussion

    Type: Azolla filiculoides Lamarck. Azolla is a genus of about ten species, four widely distributed in the New World (Svensen, 1944), ranging from the U.S. to Argentina. Identification is based largely on microscopic characters: whether the glochidia are septate or not, and the megaspore ornamentation; but since the vast majority of specimens are sterile, identification is usually uncertain. The three Oaxacan specimens seen are sterile and unable to be identified to species with certainty. They are: Camp 2764a (Fig. 127M) (NY-2 sheets), 20 km S of Oaxaca in ditch [Zimatlán ?]; Mickel 4032, Putla-Tlaxiaco, 46 km N of Putla, 44 km S of Tlaxiaco, pond, 2350 m elevation; Cruz C. 241 (ENCB), Km 33, carretera Oaxaca-Pto. Escondido, Zimatlán. A fourth specimen (Conzatti et al. 1597, vic. Oaxaca, 25 Jul 1906), reported by Conzatti (1939), has not been seen. All three species to be looked for have been reported from Mexico south to Panama, and their characters are listed below. The composite range for the genus Azolla in Mexico and Central America is: Mexico (BC, Son, Chih, Sin, Nay, Jal, Gro, Mor, Mex, DF, SLP, Hgo, Ver, Pue, Oax, Chis, Tab), Guatemala to Panama. Additional records for Azolla can often be found by checking specimens of the duckweed family (Lemnaceae) in a herbarium. The genera (Lemna, Spirodela, Wolffia and Wolffiella) often occur mixed with Azolla, sometimes with five or six species on one sheet. They have great potential for distribution by waterfowl and by human introduction (aquaria). The genus may be related to Salvinia, but the origins of both genera and their ties with other ferns, if any, are extremely remote. They appear to be relatively unchanged from their earliest known fossils of Lower Cretaceous times. References: Perkins, S. K. et al. 1985. Scanning electron microscopy of perine architecture as a taxonomic tool in the genus Azolla Lamarck. Scanning Electron Microscopy 1985(4): 1719-1734; Pieterse, A. H. et al. 1977. A comparative study of Azolla in the Netherlands. Acta Bot. Neerl. 26: 433-449; Svenson, H. K. 1944. The New World species of Azolla. Amer. Fern J. 34: 69-84.