Description: Thallus is a small (up to 10 mm or 0.4 in tall), dark olive green blade, which is infected by the fungus Guignardia alaskana M. Reed. The blades have short stalks basally, are broader than tall, often with curled edges. Cells are clustered in groups of four or more with spaces between groups of cells. Habitat: This species forms extensive carpets on supratidal bedrock of protected to exposed shores. Similar taxa: Prasiola meridionalis.