TL;DR: The green chlorococcoid algal genus Hydrianum Rabenhorst is reported for the second time in North America since its original report in 1887 and 1909, characterized by its unusual mode of sporulation.
Abstract: The green chlorococcoid algal genus Hydrianum Rabenhorst is reported for the second time in North America since its original report in 1887 and 1909. Hydrianum crassiapex was collected in Kansas, in Douglas County from a railroad trestle pond north of Lawrence and in Michigan, in Charlevoix County from Lake Geneserath. This singlecelled alga is epiphytic on macrophytes or filamentous algae, attached by means of short, hyaline stalks. Cells are asymmetrical, spherical-ellipsoid shaped in appearance. Hydrianum is characterized by its unusual mode of sporulation: zoospores are released from an apical pore while the most morphological similar genus Characium releases zoospores through a lateral pore.
TL;DR: The morphologies of 15 rare chlorococcalean algae, i.e. Hydrianum viride, Pediastrum duplex var.
Abstract: The morphologies of 15 rare chlorococcalean algae, i.e. three species of the Characiaceae [Hydrianum crassiapex Korshikov, H. viride (Scherffel) H. Ettl, Characiellopsis skujae (Fott) Komarek], four taxa of the genus Pediastrum Meyen [Pediastrum privum (Printz) E. Hegewald, P. duplex Meyen var. rugulosum Raciborski, P. angulosum (Ehrenberg) ex Meneghini, Pediastrum biradiatum Meyen], a radiococcalean alga Phacomyxa sphagnicola Skuja, Pseudodictyosphaerium fluviatile (Hindak) Hindak from the Dictyosphaeriaceae, three representatives of the family Oocystaceae (Amphikrikos minutissimus Korshikov, Gloeotaenium loitlesbergianum Hansgirg, Chlorolobion obtusum Korshikov) and three species of the genus Scenedesmus Meyen (S. ginzbergeri Kammerer, S. incrassatulus Bohlin, S. parisiensis Deflandre), are documented by drawings and micrographs and their taxonomy is discussed. Of these, Hydrianum viride, Pediastrum duplex var. rugulosum, Scenedesmus ginzbergeri and S. parisiensis are recorded for the first time in Slovakia.