Abstract
Several new genera were proposed for the classification of a number of planktonic species of Nostocales, Cyanophyceae, on the basis of the morphological and ecological characteristics and molecular sequencing. The traditional genus Anabaena is now divided into benthic Anabaena and Trichormus, and planktonic Dolichospermum and Sphaerospermopsis. The traditional genus Aphanizomenon is now divided into fascicle forming Aphanizomenon and solitary Cuspidothrix. The morphological characteristics of these four genera and several related genera of Nostocales are briefly described. The morphological and ecological characteristics of each species of Dolichospermum and Sphaerospermopsis are also compared and discussed.
