Porphyra

Porphyra is a coldwater seaweed that grows in cold, shallow seawater. More specifically, it belongs to red algae phylum of laver species (from which comes laverbread), comprising approximately 70 species. It grows in the intertidal zone, typically between the upper intertidal zone and the splash zone in cold waters of temperate oceans. In East Asia, it is used to produce the sea vegetable products "nori" (in Japan) and "gim" (in Korea). There are considered to be 60 to 70 species of "Porphyra" worldwide and seven around Britain and Ireland where it has been traditionally used to produce edible sea vegetables on the Irish Sea coast. Porphyra is a chief source of plant-based vitamin B12.
Life cycle.
"Porphyra" displays a heteromorphic alternation of generations. The thallus we see is the haploid generation; it can reproduce asexually by forming spores which grow to replicate the original thallus. It can also reproduce sexually. Both male and female gametes are formed on the one thallus. The female gametes while still on the thallus are fertilized by the released male gametes, which are non-motile. The fertilized, now diploid, carposporangia after mitosis produce spores (carpospores) which settle, then bore into shells, germinate and form a filamentous stage. This stage was originally thought to be a different species of alga, and was referred to as "Conchocelis rosea". That "Conchocelis" was the diploid stage of "Porphyra" was discovered by the British phycologist Kathleen Mary Drew-Baker in 1949 for the European species "Porphyra umbilicalis". It was later shown for species from other regions as well.
Food.
Most human cultures with access to use it as a food or somehow in the diet, making it perhaps the most domesticated of the marine algae, known as laver, (Vietnamese), "nori" (Japanese:), "amanori" (Japanese), "zakai", "gim" (Korean:), "zǐcài" (Chinese:), karengo, "sloke" or "slukos". The marine red alga "Porphyra" has been cultivated extensively in many Asian countries as an edible seaweed used to wrap the rice and fish that compose the Japanese food sushi and the Korean food "gimbap". In Japan, the annual production of "Porphyra" species is valued at 100 billion yen (US$1 billion). 
 is harvested from the coasts of Great Britain and Ireland, where it has a variety of culinary uses including laverbread. In Hawaii, "the species is considered a great delicacy, called ". Porphyra was also harvested by the Southern Kwakiutl, Haida, Seechelt, Squawmish, Nuu-chah-nulth, Nuxalk, Tsimshian, and Tlingit peoples of the North American Pacific coast.
Source of Vitamin B12.
One study in 2014 pointed to dried purple laver as a vegan source of biologically-active Vitamin B12. The study noted that B-12 was found in both raw and roasted seaweed, the latter containing about half as much—but still a sufficient amount. Just 4 grams of dried purple laver was considered sufficient to meet the RDA for B-12. However, the Academy of Nutrition and Dietetics considers this source unreliable for vegans.
Species.
Following a major reassessment of the genus in 2011, many species previously included in "Porphyra" have been transferred to "Pyropia", for example "Pyropia tenera", "Pyropia yezoensis" and the species from New Zealand "Pyropia rakiura" and "Pyropia virididentata", leaving only five species out of seventy still within "Porphyra" itself.