by Piter Kehoma Boll
If you like Japanese food, you have eaten sushi for sure, and thus have ingested the famous alga from Japanese cuisine known as nori that is used to wrap the rice, right? Well, it does not necessarily mean that you have eaten the species I am introducing today and you soon will know why.
During most of the Japan history, the main nori species used as a food was the tender nori, which is scientifically known as Pyropia tenera (formerly known as Porphyra tenera) and known in Japan as 浅草海苔 (asakusa nori). This species is a red alga and is closely related to other edible species used in other parts of the world.
The life cycle of the tender nori includes two different generations as seen in all plants. One generation, the gametophyte, is composed by haploid cells, i.e., with only one copy of each chromosome. This gametophyte stage is the largest and the one commonly used as food. It produces both female and male gametes and uses the water current to guide the male gametes, which are unable to swim, to the female gametes. For a long time, this was the only life stage known for the nori. The gametophytes were harvested in the wild, where they grow on the available substrate, especially wood. Only during the 20th century it became clear that the sporophyte, the other life stage, is smaller and needs the shell of mollusks as a substrate to grow. In fact, the sporophyte was already known, but was mistaken for a different organism classified in a genus named Conchocelis. Thus, the sporophyte is still commonly known as tie Conchocelis stage.
After the complete life-cycle of these algae was known, it did not take too long for people to develop cultivation methods that greatly increased the production of nori. Two nori strains soon became the main cultivars in Japan from around the beginning of the 1960s: Pyropia tenera var. tamatsuensis and Pyropia yezoensis f. narawaensis. The latter, as you can see, belongs to a different species of nori, the Ezo nori, known in Japan as 荒び海苔 (susabi nori).
Although the tender nori was considered of better quality and better taste, it was not as tolerant to the strong waves and winds as the Ezo nori. As a result, the Ezo nori became the favorite cultivar and spread quickly, so that this is the main species used nowadays in the Japanese cuisine. This increased cultivation of the Ezo nori displaced the original tender nori to the point that the tender nori is currently a very rare species, so rare that it is considered an endangered species by the Japanese government since 1997.
The distinction between species of Pyropia in wild populations is usually difficult because there is little morphological variation between them. Recent molecular studies from nori growing across Japan showed that the tender nori is not as rare as previously thought, although it does not makes it imune to extinction. Since the tender nori is considered softer and more tasty than the Ezo nori, there have been some attempts to increase the commercial interest on it, which could prevent it from becoming extinct in the near future.
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Niwa K, Iida S, Kato A, Kawai H, Kikuchi N, Kobiyama A, Aruga Y (2009) Genetic diversity and ingrogression in two cultivated species (Porphyra yezoensis and Porphyra tenera) and closely related wild species of Porphyra (Bangiales, Rhodophyta). Journal of Phycology 45(2): 493–502. doi: 10.1111/j.1529-8817.2009.00661.x
Niwa K, Kikuchi N, Aruga Y (2005) Morphological and molecular analysis of the endangered species Porphyra tenera (Bangiales, Rhodophyta). Journal of Phycology 41(2): 294–304. doi: 10.1111/j.1529-8817.2005.04039.x
ウィキペディア (Wikipedia in Japanese)。アサクサオリ。Available at <
https://ja.wikipedia.org/wiki/%E3%82%A2%E3%82%B5%E3%82%AF%E3%82%B5%E3%83%8E%E3%83%AA >. Access on 25 March 2019.
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* This work is licensed under a Creative Commons Attribution 2.0 Generic License.