Porphyra

Porphyra is a foliose red algal genus of about 70 species. It lives in the intertidal, typically between the upper intertidal to the splash zone. It is used to make nori, the most commonly eaten seaweed.

Porphyra
It is considered that there are 60 to 70 species of Porphyra worldwide and seven in the British Isles.

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 fertilised, now diploid, carposporangia after meiosis 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. It is now known to be the diploid stage of Porphyra. 

Food
Most human cultures with access to Porphyra use it as a food or somehow in the diet, making it perhaps the most domesticated of the marine algae, known as laver, nori, zakai, kim, karengo, sloke or slukos.

The marine red alga Porphyra, which is called nori in Japanese, 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. In Japan, the annual production of Porphyra spp. is valued at 100 billion yen (US$ 1 billion).