A contribution to the taxonomy of the nostocalean genus Richelia (Cyanophyta/Cyanobacteria)

The prokaryotic nostocalean genus Richelia JOHS. SCHMIDT 1901 (Cyanophyta/C yanobacteria) is characteristic by short trichomes with terminal heterocyte s and by the absence of akinetes. The only described species, R. intracellu laris JOHs. SCHMIDT 1901, occurs in warm oceans symbiotically in the frustu les of diatoms Rhizosolenia or Hemiaulus, or epiphytically on Chaetoceros. In this article the second species of the genus, originally described from rice fields in SE Asia as Anabaena siamensis, is transferred into the genus Richelia. The species is also characterized by short trichomes and spheric al to oval or conical terminal heterocytes, and the absence of akinetes. Pr o-heterocytes in R. siamensis are formed intercalary from one vegetative ce ll which divides into two daughter cells. The parental trichomes is broken into two daughter trichomes just at the connection of pro-heterocytes. Pro- heterocytes at the ends of trichomes are fully developed into heterocytes l ater. It is this character that separates R. siamensis from the representat ives of the genus Anabaenopsis (WOLOSZYNSKA) MILLER, in which pro-heterocyt es are formed from two neighbouring cells and ripen directly in the parenta l trichomes. Specimens similar to Anabaena siamensis have been observed in littoral of lakes, small channels and pools in Slovakia. The position of th e genus Richelia in the Nostocaceae family is discussed.