The thallus of the erect frond of Porphyra species is in the form of a flat, lanceolate or broadly elliptical blade. The fronds are composed entirely of either small rectangular or rounded cells which are arranged in one or, more rarely, two cell layers. They are dark purplish to brownish red. In the wild, Porphyra species normally grow attached to rocks or as epiphytes in the intertidal or shallow subtidal and are generally highly seasonal in their appearance and growth.
There are about 16 species of Porphyra growing on the coast of Korea.
Common cultivated strains of Porphyra in Korea are: Porphyra yezoensis, P. tenera and P. kuniedae (Kang 1972). Since 1980, many strains have been introduced from Japan in a free-living conchocelis condition. These new strains have contributed to the increased production of Porphyra in Korea but not to its quality. The current trend in the Porphyra industry is towards harvest of wild P. kuniedae, P. dentata and P. seriata at the south-west coast, owing to the high market price of its dried laver.
Cultivation history of seaweed began with Porphyra. According to the oldest records on Porphyra the alga was processed by chopping and drying earlier than 1425 (Bae 1991). Another story, passed from generation to generation, tells that it was in 1623-1649 that Porphyra was cultivated around Taein Island when a fisherman found some floating bamboo twigs with Porphyra attached to them and began his own cultivation by planting bamboo twigs along the sea shore (Kang and Koh 1977). This bambo twig cultivation method was used until 1986 around Taein Island and its vicinity on the south coast. The method is no longer in use.
Seeding of Porphyra is usually done in March or April. Oyster shells are used as they can be obtained cheaply and easily from oyster culture grounds. The conchocelis filaments grow densely within these shells. The seeding shells are laid and cultured on the floor of shallow concrete tanks or wooden boxes which are covered with polyethylene film. Alternatively the oyster shells may be tied into string in sets of 10 and dangled from rods to be suspended in deep tanks of seawater. Cultivation nets are seeded with spores from the conchocelis phase within the oyster shells from late September to early October. During this period, the seawater temperature begins to drop below 22-23℃. The temperature during this period is variable depending on where the cultivation grounds are located.
Oyster shells, containing the Porphyra conchocelis, are applied to groups of cultivation nets (30-50 nets, approximately 1.8×4m in size), which are tied to bamboo or PVC frames. Each set of nets has about 100 shells laid on top, then all of the nets are covered with a polyethylene envelope (Sohn and Kain 1989a). Modified methods are being implemented mainly in the south-west region. Large sections of net (approximately 1.8×20m) are grouped into larger sheets (1.8×40m). Then about 150 oyster shells are crushed into small pieces and enclosed in a slender polyethylene sac which is placed on each set of cultivation nets.