Phycocalidia suborbiculata is a red alga which grows as a single sheet or blade, one cell thick, and, often notched or rumpled along the edges, attached by a rhizoidal holdfast, and growing singly or in clusters, often on rocks, limpets, or barnacles in the upper intertidal. The thalli reach 40 mm by 25 mm, and are brown to red. The season of occurrence varies over its wide range, year round in North Carolina, summer in New England and Japan, winter and spring in Spain, and spring and summer in California. This alga is native from Japan and China to India and Indonesia. It may be cryptogenic in Australia and New Zealand. It was collected in North Carolina in 1947, and in Delaware in 1966. On the East Coast, it ranges from Florida to Maine, but is probably often overlooked,. On the West Coast, P. suborbiculata was found in Baja California, Mexico in 1986, in Tomales Bay in 2011, and in San Francisco Bay in 2011. This alga has been widely introduced around the world, in 1995 in the Canary Islands, in 2010 in mainland Spain, and 1985 in Brazil, Phycocalidia suborbiculata belongs to a. group of sheet-like red algae, some of which (Pyropia spp) are cultivated and eaten as 'nori', Possible vectors include algal aquaculture, transplants of Pacific oysters, ballast water, and fouling. However, no impacts have been reported.