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.