The morphology and ecology of a†new species of the cyanophyte/cyanobacterial genus Aphanizomenon Morren ex Bornet etFlahault, A. slovenicum Rekar et Hindák, are described from Lake Bled, NW Slovenia. The species produced a heavy waterbloom in May - December 1997 but disappeared during 1998. Macroscopic flakes of bundles of trichomes similar to A. flos-aquae (L.) Ralfs ex Bornet et Flahault formed in a layer between 10 - 20 m depth. They differed from A. flos-aquae by shorter and narrow short cylindrical to barrel-shaped cells, and by trichomes that sometimes consisted of morphologically different cell sections. Maximum abundance was found in August : 655 trichomes.m1-1. Heterocytes were occasionally present and akinetes have been observed only in laboratory cultures. The main characteristics of the investigated cultures of A. slovenicum and A.flos-aquae isolated from a fishpond at Ledava (NE Slovenia) are given.
